An average of 18 customers arrive at a service center each hour. There are two servers on duty,
and each server can process 12 customers per hour.
(1) What is the system utilization?
(2) What is the average number of customers in the system (waiting plus being served)?
(3) What is the average time customers wait in line for service?
(4) What is the average waiting time for customers who actually have to wait?