The key is 'binary operator' - you should use

```
#ifndef RATIONALNUMBER_H
#define RATIONALNUMBER_H
using namespace std;
// foward declaration
RationalNumber operator/ (const RationalNumber& l, const RationalNumer& r);
class RationalNumber
{
// 'friend' is only necessary for non-members
friend RationalNumber operator/ (const RationalNumber& l, const RationalNumer& r);
public:
RationalNumber(int numerator, int denominator);
System::String^ toString();
int getNumerator();
int getDenominator();
RationalNumber operator+ (const RationalNumber& r) const;
RationalNumber operator- (const RationalNumber& r) const;
RationalNumber operator/ (const RationalNumber& r) const;
RationalNumber operator* (const RationalNumber& r) const;
private:
int _numerator;
int _denominator;
int _wholeNumber;
bool isValidDenominator(const int denominator);
void simplifyFraction();
};
#endif
// ...
RationalNumber operator/ (const RationalNumber& l, const RationalNumer& r);
{
// implement here
}
```