In the first 2 hours after meadow's self-service laundry opens, m large washing machines and n small washing machines are in continual use. including the time for filling and emptying the washing machines, each load of laundry takes 30 minutes in a large washing machine and 20 minutes in a small washing machine. what is the total number of loads of laundry done at meadow's self-service laundry during this 2-hour period?