If one child bought a ticket, we would calculate the total cost by multiplying $4.50 by 1. If two children bought tickets, we could calculate the total cost by multiplying the total cost by 2. So, the total number of tickets will always be 4.50 * the total number of tickets.
Because the number of children who bought tickets is represented by c and the number of adults who bought tickets are represented by a, our equation should look like:
$4.50c + $4.50a = money earned
