class A 

{

    public int Foo() { ...some logic here... }   

}

​

class B

{

    public int Bar() 

    {

        A a = new A();

        int result = a.Foo();

        return result * 3;

    }

}

​

static void Main(string[] args)

{

    B b = new B();

    int result = b.Bar();

    Console.WriteLine(result);

}