We have everything done except we do not know how to do the adding of rational numbers. can you help?

Code:

#include "Rational.h"
#include "math.h"
#include <iostream>
using namespace std;
Rational::Rational()
{
numerator = denominator = 1;
}
Rational::Rational(int N, int D)
{
numerator = N;
denominator = D;
}
int Rational::getN()
{
return numerator;
}
int Rational::getD()
{
return denominator;
}
int Rational::multiply(Rational rational2)
{
int finalN =getN()*rational2.getN();
int finalD =getD()*rational2.getD();
Rational rational(finalN,finalD);
simplify(rational);
}
int Rational::divide(Rational rational2)
{
int finalN =getN()*rational2.getD();
int finalD =getD()*rational2.getN();
Rational rational(finalN,finalD);
simplify(rational);
}
int Rational::add(Rational rational2)
{
int tempN = getN()*rational2.getD();
int tempD = getD()*rational2.getN();
int finalN = tempN*tempD
int finalD =
Rational rational(finalN,finalD);
simplify(rational);
}
void Rational::simplify(Rational rational)
{
int x=rational.getN();
int y=rational.getD();
int z;
while (y!=0)
{
z=x%y;
x=y;
y=z;
}
int finalN=rational.getN()/x;
int finalD=rational.getD()/x;
Rational rationalnew (finalN,finalD);
cout <<finalN<<"/"<<finalD<<endl;
}
bool Rational::compare(Rational rational2)
{
float initial=(float)getN()/getD();
float final= (float)rational2.getN()/rational2.getD();
if (initial==final) return true;
else return false;
}