Problem # $2(10$ points$)$

A company having a large group of employees must decide if it needs another photocopying machine. The cost of a machine is $$40$ per $8-$hour day whether or the machine is in use. An average of $4$ employees per hour need to use the copying machine. Each employee uses the copier for an average of $10$ minutes. Interarrival times and copying times are exponentially distributed. Employees are paid $$8$ per hour, and we assume that a waiting cost is incurred when a worker is waiting in line or is using the copying machine. How many copying machines should the company rent?