Five student government officers want to go to the state convention. It will cost them $115 for registration, $365 for transportation and food, and $55 per person for the hotel. There is $485 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 $6 per car, how many cars must they wash in order to have enough money to pay for the trip?