a retail chain has 4 stores in a region supplied from 2 supply sources. trucks have a capacity of 20,000 units and cost $500 per shipment plus $50 per stop. the cost of holding one unit in inventory at retail for a year is $0.10. the annual sales for each product at each retail store are 480,000 units and are pretty stable. the vp of the supply chain is considering a direct-shipping model. please answer the following questions.