Consider the RationalNumber class declaration below. You need to write four functions: - A stand alone friend function that overloads the << operator and prints a rational number in the form numerator/denominator. - A member function that overloads the subtraction operator (-) for the RationalNumber class. The member function subtracts two RationalNumber objects r1 and r2 and assigns the result to object r3. - A standalone friend function that overloads the postfix increment operator ( ) for the RationalNumber class. The friend function adds one to a RationalNumber object and allows cascaded function calls. - A stand alone friend function that overloads the >> stream extraction operator and prompts the user for rational number (numerator and denominator)