diff --git a/Homeworks/Answer.php b/Homeworks/Answer.php
new file mode 100644
index 0000000..f1c0e63
--- /dev/null
+++ b/Homeworks/Answer.php
@@ -0,0 +1,437 @@
+<?php
+
+/**Dinh Van Tai*/
+
+/**
+    * 1. Substitute Algorithm
+*/
+function foundPerson(array $people)
+{
+    for ($i = 0; $i < count($people); $i++) {
+        if ($people[$i] == 'Don') {
+            return 'Don';
+        }
+        if ($people[$i] == 'John') {
+            return 'John';
+        }
+        if ($people[$i] =='Kent') {
+            return 'Kent';
+        }
+    }
+
+    return '';
+}
+
+// Refactor
+function foundPerson(array $people)
+{
+    foreach (['Don', 'John', 'Kent'] as $needle) {
+        if (in_array($needle, $people) {
+            return $needle;
+        }
+    }
+
+    return '';
+}
+
+/**
+    * 2.Replace Nested Conditional with Guard Clauses
+*/
+public function getPayAmount() {
+    if ($this->isDead) {
+        $result = $this->deadAmount();
+    } elseif ($this->isSeparated) {
+        $result = $this->separatedAmount();
+    } elseif ($this->isRetired) {
+        $result = $this->retiredAmount();
+    } else {
+        $result = $this->normalPayAmount();
+    }
+
+    return $result;
+}
+
+// Refactor
+public function getPayAmount() {
+    if ($this->isDead) {
+        return $this->deadAmount();
+    }
+    if ($this->isSeparated) {
+        return $this->separatedAmount();
+    }
+    if ($this->isRetired) {
+        return $this->retiredAmount();
+    }
+
+    return $this->normalPayAmount();
+}
+
+/**
+    * 3. Replace Conditional with Polymorphism
+*/
+class Bird
+{
+    public function getSpeed() {
+        switch ($this->type) {
+            case 'EUROPEAN':
+                return $this->getBaseSpeed();
+            case 'AFRICAN':
+                return $this->getBaseSpeed() - $this->getLoadFactor() * $this->numberOfCoconuts;
+            case 'NORWEGIAN_BLUE':
+                return ($this->isNailed) ? 0 : $this->getBaseSpeed($this->voltage);
+        }
+        throw new Exception('Should be unreachable');
+    }
+}
+
+// Refactor
+abstract class Bird
+{
+    abstract public function getSpeed();
+}
+
+class European extends Bird
+{
+    public function getSpeed()
+    {
+        return $this->getBaseSpeed();
+    }
+}
+class African extends Bird
+{
+    function getSpeed()
+    {
+        return $this->getBaseSpeed() - $this->getLoadFactor() * $this->numberOfCoconuts;
+    }
+}
+class NorwegianBlue extends Bird
+{
+    function getSpeed()
+    {
+        return ($this->isNailed) ? 0 : $this->getBaseSpeed($this->voltage);
+    }
+}
+
+
+/**Vu Xuan Truong*/
+
+/**
+    * 4. Long Method
+*/
+
+function printPerfectBoy() {
+
+    //print menu
+    print("************************");
+    print("********* Menu *********");
+    print("************************");
+
+    // Perfect Boy = Gender(Boy) + mathPerfect + englishPerfect ;
+    if ($this->gender == 1 && $this->getMathScore() > 8 && $this->getEnglishScore > 8) {
+        //print details
+        print("Student name:  " . $this->name);
+        print("Student math score : " . this->getMathScore());
+        print("Student english score : " . this->getEnglishScore());
+    }
+}
+
+// Refactor (Extract Method):
+
+function printPerfectBoy() {
+    $this->printMenu();
+
+    // Perfect Boy = Gender(Boy) + mathPerfect + englishPerfect ;
+    if ($this->isBoy() && $this->getMathScore() > 8 && $this->getEnglishScore > 8) {
+        $this->printDetails();
+    }
+}
+
+function isBoy() {
+    return $this->getGender == 1;
+}
+function printMenu() {
+    print("************************");
+    print("********* Menu *********");
+    print("************************");
+}
+function printDetails () {
+    print("Student name:  " . $this->name);
+    print("Student math score : " . this->getMathScore());
+    print("Student english score : " . this->getEnglishScore());
+}
+
+/**
+    * 5. Comment
+*/
+
+function printPerfectBoy() {
+    $this->printMenu();
+
+    // Perfect Boy = Gender(Boy) + mathPerfect + englishPerfect ;
+    if ($this->isBoy() && $this->getMathScore() > 8 && $this->getEnglishScore > 8) {
+        $this->printDetails();
+    }
+}
+
+// Refactor (Extract Variable) :
+
+function printBestBoy() {
+    $this->printMenu();
+
+    $isBoy = $this->gender == 1;
+    $isMathPerfect = $this->getMathScore() > 8;
+    $isEnglishPerfect = $this->getEnglishScore() > 8;
+    if ($isBoy && $isMathPerfect && $isEnglishPerfect) {
+        $this->printDetails($this->getScore());
+    }
+}
+
+
+/**
+    * 6. Primitive Obsession
+*/
+
+function printBestBoy() {
+    $this->printMenu();
+
+    $isBoy = $this->gender == 1;
+    $isMathPerfect = $this->getMathScore() > 8;
+    $isEnglishPerfect = $this->getEnglishScore() > 8;
+    if ($isBoy && $isMathPerfect && $isEnglishPerfect) {
+        $this->printDetails($this->getScore());
+    }
+}
+
+//Refactor (Replace Data Value with Object):
+
+class ScoreType {
+    const PERFECT = 8;
+    function getPerfect() {
+        return PERFECT;
+    }
+}
+class Student {
+    const BOY = 1;
+    function isBoy() {
+        return $this->getGender == BOY;
+    }
+    function printBestBoy() {
+        $this->printMenu();
+
+        $scoreType = new ScoreType();
+        $isMathPerfect = $this->getMathScore() > $scoreType->getPerfect();
+        $isEnglishPerfect = $this->getEnglishScore > $scoreType->getPerfect();
+        if ($this->isBoy() && $isMathPerfect && $isEnglishPerfect) {
+            $this->printDetails($this->getScore());
+        }
+    }
+}
+
+
+/* Ngo Trung Thang */
+
+/**
+    * 7. Long Parameter List
+*/
+function showInfo($height, $weight, $gender, $class, $address)
+{
+    echo $height;
+    echo $weight;
+    echo $gender;
+    echo $class;
+    echo $address;
+}
+
+//refactor
+function showInfo($data)
+{
+    echo $data['height'];
+    echo $data['weight'];
+    echo $data['gender'];
+    echo $data['class'];
+    echo $data['address'];
+}
+
+/**
+    * 8. Long Method
+*/
+class Order
+{
+    public function calculate()
+    {
+        $details = $this->getOrderDetails();
+        foreach ($details as $detail) {
+            if (!$detail->hasVat()) {
+                $vat = $this->getCustomer()->getVat();
+            } else {
+                $vat = $detail->getVat();
+            }
+            $price = $detail->getAmount() * $detail->getPrice();
+            $total += $price + ($price / 100 * $vat->getValue());
+        }
+        if ($this->hasDiscount()) {
+            $total = $total–($total / 100 * $this->getDiscount());
+        } elseif ($this->getCustomer()->hasDiscountForMaxAmount() && $total >= $this->getCustomer()->getMaxAmountForDiscount()) {
+            $total = $total–($total / 100 * $this->getCustomer()->getDiscountForMaxAmount());
+        }
+
+        return $total;
+    }
+}
+
+//refactor
+class Order
+{
+    private function calculateDetailsPrice()
+    {
+        foreach ($this->getOrderDetails() as $detail) {
+            if (!$detail->hasVat()) {
+                $vat = $this->getCustomer()->getVat();
+            } else {
+                $vat = $detail->getVat();
+            }
+            $price = $detail->getAmount() * $detail->getPrice();
+            $total += $price + ($price/100 * $vat->getValue());
+        }
+
+        return $total;
+    }
+
+    private function applyDiscount($total)
+    {
+        if ($this->hasDiscount()) {
+            $total = $total - ($total/100 * $this->getDiscount());
+        } elseif ($this->getCustomer()->hasDiscountForMaxAmount() &&
+            $total >= $this->getCustomer()->getMaxAmountForDiscount()) {
+            $total = $total - ($total/100 * $this->getCustomer()->getDiscountForMaxAmount());
+        }
+
+        return $total;
+    }
+    public function calculate()
+    {
+        return $this->applyDiscount($this->calculateDetailsPrice());
+    }
+}
+
+/**
+    * 9. Duplicate Code
+*/
+
+class Customer extends Person
+{
+    public function getAge()
+    {
+        return date('Y') - date('Y', strtotime("2010-12-17"));
+    }
+}
+
+class Vendor extends Person
+{
+    public function getAge()
+    {
+        return date('Y') - date('Y', strtotime("2010-12-17"));
+    }
+}
+
+//refactor
+class Person
+{
+    public function getAge()
+    {
+        return date('Y') - date('Y', strtotime("2000-11-25"));
+    }
+}
+
+class Customer extends Person
+{
+//
+}
+
+class Vendor extends Person
+{
+//
+}
+
+/** Pham Viet Toan */
+
+/**
+ * 10. Data clump
+ */
+$name = $person->getName();
+$age = $person->getAge();
+$getPerson = $persons->find($name, $age);
+
+//refactor
+$getPerson = $person->find($person);
+
+/**
+ * 11. Temporary field -replace method with method object
+ */
+
+class Order {
+    public function sendMail() {
+        $name = 'Pham Viet Toan';
+        $email = 'viettoan290696@gmail.com';
+        $age = 22;
+        $price = 100;
+        // long computation.
+    }
+}
+
+//refactor
+class Order {
+    public function sendMail() {
+        return new Mail($this)->send();
+    }
+}
+
+class Mail {
+    private $name;
+    private $email;
+    private $age;
+    private $price;
+
+    public __construct(Order $order) {
+        // copy relevant information from order object.
+    }
+
+    public function send() {
+        // long computation.
+    }
+}
+
+/**
+ * 12. Refused bequest - extract superclass
+ */
+
+class Department {
+
+    public function getCount() {}
+
+    public function getName() {}
+
+    public function getPlace() {}
+}
+
+class Employee {
+    public function getName() {}
+
+    public function getId() {}
+}
+
+ //refactor
+
+class Party {
+    public function getName() {}
+}
+
+class Department extends Party {
+    public function getCount() {}
+
+    public function getPlace() {}
+}
+
+class Employee extends Party {
+    public function getId() {}
+}