The illustration shows a "Function call.” The lines of code and the annotations are as follows:

"int main()
{
double price, bill;
int number;
cout << "Enter the number of items purchased: ";
cin >> number;
cout << "Enter the price per item $";
cin >> price;" with the “cout” and “cin” statements annotated as "1. Before the function is called, values of the variables number and price are set to 2 and 10.10, by cin statements (as you can see the Sample Dialogue in Display 4.3)."
"bill = totalCost (number, price);" annotated as "2. The function call executes and the value of number (which is 2) plugged in for numberPar and value of price (which is 10.10) plugged in for pricePar."
"cout.setf (ios::fixed);
cout.setf (ios::showpoint);
cout.precision(2);
cout << number << " items at "
<< "$" << price << " each.\n"
<< "Final bill, including tax, is $" << bill
<< endl;
return 0;
}
double totalCost (int numberPar, double pricePar)"
"{
const double TAX_RATE = 0.05; //5% sales tax
double subtotal;" annotated as "3. The body of the function executes with numberPar set to 2 and pricePar set to 10.10, producing the value 20.20 in subtotal."
"subtotal = pricePar * numberPar;
return (subtotal + subtotal * TAX_RATE);
}" annotated as "4. When the return statement is executed, the value of the expression after return is evaluated and returned by the function. In this case, (subtotal + subtotal * TAX_RATE) is (20.20 + 20.20*0.05) or 21.21" and “5. The value 21.21 is returned to where the function was invoked. The result is that totalCost (number, price) is replaced by the return value of 21.21. The value of bill (on the left-hand side of the equal sign) is set equal to 21.21 when the statement bill = totalCost(number, price); finally ends.”
There are arrows  from "number" and "price" in line "bill = totalCost (number, price);" pointing to "numberPar" and "pricePar" in line "double totalCost (int numberPar, double pricePar)," labeled  “2” and “10.10” repectively. Another arrow from “return (subtotal + subtotal * TAX_RATE);” is pointing to “totalCost (number, price);” with value “21.21.” The total value in the line “return (subtotal + subtotal * TAX_RATE);” is labeled “21.21.”