A fast food chain is designing a new location and needs to determine how much driveway space to allow for cars waiting to drive up to the service window. The drive-thru service will have 3 pick-up windows and a single waiting line. At another location in a similar setting, the average service time is 4 minutes per customer and average arrival rate is 36 customers per hour. It is expected that the new location will have similar characteristics. What is the expected average number of cars in the system