The Decision Sciences Department is trying to determine whether to rent a slow or a fast copier. The department believes that an employee's time is wbrth dollar 15 per hour. The slow copier rents for dollar 4 per hour and it takes an employee an average of 10 minutes to complete copying (exponentially distributed). The fast copier rents for dollar 15 per hour and it takes an employee an average of 6 minutes to complete copying. An average of 4 employees per hour need to use the copying machine (interarrival times are exponential). Which machine should the department rent?