Trucks arrive at your warehouse at the rate of 15 per hour during business hours. Crews can unload trucks at the rate of 5 trucks per hour. Your employees recently received a significant pay raise due to settling a contract dispute and you’re re-examining the question of how many crews to use. Your new rates are crew and dock cost of $100 per hour and a driver cost of $120 per hour. Determine which number of crews; 4, 5, 6 or 7 will minimize your total cost.