Major appliances are assembled on a production line at the rate of 55 per hour. The products are moved along the line on work pallets (one product per pallet). At the final workstation the finished products are removed from the pallets. The pallets are then removed from the line and delivered back to the front of the line for reuse. Automated guided vehicles are used to transport the pallets to the front of the line; a distance of 600 ft. Return trip distance (empty) to the end of the line is also 600 ft. Each AGV carries four pallets and travels at a speed of 150 ft/min (either loaded or empty). The pallets form queues at each end of the line, so that neither the production line nor the AGVs are ever starved for pallets. Time required to load each pallet onto an AGV = 15 sec; time to release a loaded AGV and move an empty AGV into position for loading at the end of the line = 12 sec. The same times apply for pallet handling and release/positioning at the unload station located at the front of the production line. Assume the traffic factor is 1.0 since the route is a simple loop. How many vehicles are needed to operate the AGV system?