How to get resultant type of multiplying two different types

How would one go about getting the resultant type of multiplying two different types i.e.

template< typename TA, typename TB>
struct multiplier
{
    using result_type = // something here finds result of TA*TB
    result_type operator()( TA a, TB b ) const
    {
        return a * b;
    }
};

I know in C++ it is perfectly valid to multiply two numerical values of different type and this will give a value in a type that is known to the compiler. I.e. multiplying a double and an int will result in a double type answer.

As such in a templated class where the types are known at compile-time it should be possible to determine the type that will be created. Indeed a lambda can be created to return the result of this value i.e.

auto foo = [](int a, float b){ return a*b;}
auto c = foo( 13, 42.0 );

This would cause c to be a float.

Please note that I am limited to being able to use only features of C++11 or below.