expression cant be called as a function : error

I am facing a compile time error here.

I tried to find solution to the error but cant reach a conclusion.

It says "expression cant be called as a function" when I am trying to return value using parenthesis in a user defined function.

My code is:

template <class t1>
t1 sum(t1 a, t1 b)
{
    if (a != b)
    {
        return a + b;
    }
    else
    {
        return 3(a+b);
    }
}

>Solution :

3(a+b) means nothing for a C++ compiler. If you are trying to multiply, use 3*(a+b). If 3 is a function, change its name, you can’t use a number as a function name.