using System;

public class Program

{

    public static void Main()

    {

        MathClass math = new MathClass();

        int answer = math.Add(5, 5);

        Console.WriteLine(answer); //Should print 10

​

        answer = math.Multiply(5, 5);

        Console.WriteLine(answer); //Should print 25

        Console.WriteLine("Any key to continue");

        Console.ReadLine();

    }

}

​

public class MathClass

{   

    public int Add(int a, int b)

    {

        return a + b;

    }

}

​

public static class MathExtensions

{

    public static int Multiply(this MathClass i, int value1, int value2)

    {

        return value1*value2;

    }

}