Six student government officers want to go to the state convention. It will cost them $100 for registration, $380 for transportation and food, and $54 per person for the hotel. There is $500 budgeted for the convention in the student government savings account. They can earn the rest of the money they need by having a car wash. If they charge $5 per car, how many cars must they wash in order to have enough money to pay for the trip?