The manager of a large group of employees must decide if she needs another copying machine. The cost of a machine is $275 per 8-hour day whether or not the machine is in use. An average of 16.5 people per hour need to use the copying machine. Each person uses the copier for an average of 3.5 minutes. The employee cost is $31 per hour, and we assume that a waiting cost is incurred when a worker is waiting in line. How many copying machines should be rented to minimize cost?