The area of a parking lot is 600 square meters. A car requires 6 square meters. A bus requires 30 square meters. The attendant can handle only 60 vehicles. The parking lot also needs to be able to hold at least 3 buses and 10 cars. A car is charged $2.50 each day and a bus is charged $7.50 each day. They want to collect at least $75 each day.