Need help declaring a value for "cash". - c++

Question

it says in the instruction "you may assume the cash to be equal or greater than the total bill". How do I declare a value for cash and make it greater than or equal to the total bill? Is my declaration of the variables for "change" "totalBill" are correct? I really need some help and like I said this is my first time.
#include <iostream>
#include <iomanip>
using namespace std;
const double CHILDPRICE = 10.00;
const double ADULTPRICE = 20.50;
int main ()
{
double adultTotal, childTotal, totalBill, change;
int childTix, adultTix, cash;
cout << "\n Chesapeake Amusement Park" << endl << endl;
cout << " Enter children tickets... ";
cin >> childTix;
cout << " Enter adult tickets...... ";
cin >> adultTix;
childTotal = CHILDPRICE * childTix;
adultTotal = ADULTPRICE * adultTix;
totalBill = childTotal + adultTotal;
change = cash - totalBill;
//The following is a sample of how you can format the output
//childTix is an integer variable
//CHILDPRICE is a double const
//childTotal is a double variable
cout.setf(ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);
cout << "\n\n Chesapeake Amusement Park";
cout << "\n -------------------------";
cout << "\n\n Tickets Price Total\n";
cout << " Children " << setw(3) << childTix
<< setw(14) << CHILDPRICE
<< setw(11) << childTotal;
cout << "\n Adults " << setw(3) << adultTix
<< setw(14) << ADULTPRICE
<< setw(11) << adultTotal;
cout << "\n ";
cout << "\n ";
cout << "\n Total Bill " << setw(11) << totalBill;
//Place remaining input/output statements here
cout << "\n ";
cout << "\n ";
cout << "\n Cash recieved...... ";
cin >> cash;
cout << "\n ";
cout << "\n ";
cout << "\n Change " << setw(4) << change;
return 0;
}