Trucks arrive at a warehouse at a rate of $15$ per hour during

business hours. Crews can unload the trucks at a rate of five per

hour. The high unloading rate is due to cargo being containerized.

Recent changes in wage rates have caused the warehouse manager

to reexamine the question of how many crews to use. The new rates

are: Crew and dock cost is $$100$ per hour; truck and driver cost is

$$120$ per hour.