Done

Boolean.CSharp.Main/Core.cs

@@ -30,7 +30,7 @@ public Car(string Make)
                 }
             */
 
-            Car car = new Car("Volkswagen");
+            Car car = new Car("Volkswagen","Beetle");
             /*  When the car in instantiated, the constructor is passed a string
              in this case Volkswagen which is a Make of car is passed in.
              Within the constructor the 'string Make' variable has scope within the constructor and assiged to the _make member now visible to the whole class
@@ -132,10 +132,11 @@ What are the parameters and types?
              */
             Aeroplane plane = new Aeroplane();            
             plane.FlightDetails("LHR", "JFK");
-            
+
             //TODO:  5.  Call the FlightDetails method that sets the cancelled message and  cancel the flight
-
-           //write code here 
+
+            //write code here 
+            plane.FlightDetails("Flight is canceled");
 
             return plane;
         }

Boolean.CSharp.Main/Extension.cs

@@ -12,18 +12,51 @@ public class Extension
         //Implement the following methods:
 
         //TODO: 1. add, which accepts two floats and returns a float (both floats added together)
+        public float add(float valueOne, float valueTwo) {
+            return valueOne + valueTwo;
+        }
 
         //TODO: 2. add, which accepts two doubles and returns a double (both doubles added together)
-
-        //TODO: 3. subtract, which accepts two floats and returns a float (first float minus second float)      
-
-        //TODO: 4. subtract, which accepts a String and a char and returns a string with all instances of the provided char removed        
+        public double add(double valueOne, double valueTwo) {
+            return valueOne + valueTwo;
+        }
+
+        //TODO: 3. subtract, which accepts two floats and returns a float (first float minus second float)
+        public float subtract (float valueOne, float valueTwo) {  
+            return valueOne - valueTwo;
+        }
+
+        //TODO: 4. subtract, which accepts a String and a char and returns a string with all instances of the provided char removed
+        public string subtract(string s, char charToRemove)
+        {
+            s = s.Replace(charToRemove.ToString(), ""); 
+            return s;
+        }
 
         //TODO: 5. multiply, which accepts two ints and returns an int (first int multiplied by second int)
+        public int multiply (int valueOne, int valueTwo) {  return valueOne * valueTwo; }
 
         //TODO: 6. multiply, which accepts a string and an int, and returns a string containing the provided string as many times as the provided int separated by a comma. E.g. multiply("Hello", 3) -> "Hello,Hello,Hello"
-
+        public string multiply (string s, int nrOfTimes) {
+            string returnS ="";
+            for (int i = 0; i < nrOfTimes; i++)
+            {
+                if(returnS.Length == 0) returnS += s;
+                else returnS += ',' + s; 
+            }
+            return returnS;
+        }
+
         //TODO: 7. multiply, which accepts an array of Strings that each contain a number, and an int. The method should return an array of ints that contain the value of multiplying each String number by the provided int E.g. multiply(["2", "7", "3"], 3) -> [6, 21, 9]
+        public int[] multiply(string[] stringArr, int multiplier)
+        {
+            int[] intArr = new int[stringArr.Length];
+            for (int i = 0; i < stringArr.Length; i++)
+            {
+                intArr[i] = int.Parse(stringArr[i]) * multiplier;
+            }
+            return intArr;
+        }
 
     }
 }

Boolean.CSharp.Main/Misc/Bicycle.cs

@@ -10,6 +10,11 @@ public class Bicycle
     {
         private int _wheelCount;
 
-        public int WheelCount { get; set; }
+        public Bicycle(int wheelCount =2)
+        {
+            _wheelCount = wheelCount;
+        }
+
+        public int WheelCount { get { return _wheelCount;  } }
     }
 }

Boolean.CSharp.Main/Misc/Car.cs

@@ -22,9 +22,17 @@ public Car(string Make)
             _make = Make;
             _model = string.Empty;
         }
+        public Car(string Make, string Model)
+        {
+            _make = Make;
+            _model = Model;
+        }
+
+        //public string Make { get => _make; set => _make = value; }
+        //public string Model { get => _model; set => _model = value; }
 
-        public string Make { get => _make; set => _make = value; }
-        public string Model { get => _model; set => _model = value; }
+        public string Make { get { return _make; } }
+        public string Model { get { return _model; } }
 
     }
 }

Boolean.CSharp.Main/Misc/Motorbike.cs

@@ -21,14 +21,15 @@ public Motorbike()
             _model = string.Empty;
         }
         public Motorbike(string Make, string Model)
-        {            
+        {
+            _cc = 373; 
             _make = Make;
             _model = Model;         
 
         }
         public string Make { get; }
         public string Model { get; }
-        public int CC { get; }
+        public int CC { get { return _cc; } }
 
     }
 }

Boolean.CSharp.Main/Misc/Unicycle.cs

@@ -10,6 +10,11 @@ public class Unicycle
     {
         private string _nameOfUnicyclist;
 
+        public Unicycle()
+        {
+            _nameOfUnicyclist = "Linus";
+        }
+
         public string NameOfUnicyclist { get => _nameOfUnicyclist; set => _nameOfUnicyclist = value; }
         public int WheelCount { get; set; } = 1;
     }