Carla is dividing up chores for her two kids, Anna and Billy. She wants each of them to spend the same number of minutes working. Sweeping takes 3 minutes per room, washing the dishes takes 2 minutes per dish, and doing laundry takes 9 minutes per load. If Anna does the sweeping for 10 rooms and Billy does two loads of laundry, how many dishes should Billy wash so they spend the same amount of time doing chores?
Give me a clear explanation.