using System;

public static class MathClass

    {

        public static int Add(this int a,int b)

        {

            return a+b;

        }

     public static int Multiply(this int a,int b)

        {

            return a*b;

        }

    }  

public class Program

{

    public static void Main()

    {

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

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

    answer = MathClass.Multiply(5, 5);

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

​

    }

}