Ben Barnesworth looks over his distribution center where he ships out books, and some other related items, to customers across the country. Books arrive to his distribution center usually from large book wholesalers but sometimes directly from the manufacturer. The books are stored on shelves. Each book is placed carefully in a precise location determined by their ware$-$ house management system.

Orders arrive through their web site and are transmitted to their ware$-$ house management system. Order pickers walk the aisles using hand held devices with a display that directs them to the items to be picked for each customer order. After a picker completes all items for a customer order, the picked order is placed into a tote on a conveyor. The conveyor then transfers the order to the packing department. There a group of packers place each customer order into a box, add packing material, seal and label the box and then place the box on a conveyor. A bar code on the box label directs the package automatically to the correct shipping lanes $$ Fed Ex$,$ UPS, or USPS.

Ben$$s distribution center is located in Lexington, KY$.$ This means that if he wants to get an order to a customer on the West or East Coast overnight he must use Fed Ex$.$ To get an order to the coasts in two days can be accomplished by priority UPS. Standard UPS ground rates $($generally the most economical$)$ will take $3-4$ days. He knows some customers don$$t mind, and others are willing to pay higher rates for overnight delivery. But he also knows that many customers visit his web site, select b