$18\mathrm{.}3-3.*$ Tim Madsen is the purchasing agent for Computer Center,

a large discount computer store. He has recently added the hottest

new computer, the Power model, to the store$$s stock of goods. Sales

of this model now are running at about $13$ per week. Tim purchases

these computers directly from the manufacturer at a unit cost of

$$3,000,$ where each shipment takes half a week to arrive.