A freight truck has to be loaded with 70000 ft³ of a special material available at a certain location. Because the truck has no access to this location, a specially equipped loading device is used to load the material onto self-powered platform trucks, which the transport the material to the freight truck parked at a nearby location that is accessible. Whereas the loading device costs $1000 each hour to rent, the platform trucks can be rented for only $100 per hour each. There is no limit on the number of platform trucks that can be rented. Each platform truck can hold 400 ft3 of the material, and it takes an average of 5 minutes for it to haul the material, unload it on the freight truck, and return to the location for the next delivery. Due to the space restrictions, loading equipment design, and other reasons, the loading itself requires an average of 12 minutes.
a) Identify the waiting system in which the platform trucks are servers.