A customer orders two items from an online US retailer with a large network of warehouses. Some Warehouses are very large, containing the full assortment of items. Other Warehouses are smaller, closer to customers, and contain an assortment of only the popular items. As an approximation, there are about 18 large Warehouses, and about 150 smaller Warehouses. The large Warehouses contain about 10 million SKUs, and the smaller Warehouses stock about 100,000 SKUs each. Suppose that the path of a product after receiving an order is to immediately pack it at the warehouse where the product is stocked, ship it to the last mile processing center, and then ship it to the customer in a local delivery van. Assume that there is a cost to process an item in a Warehouse, which may be different for different Warehouses. Assume there is a cost to ship the item from a Warehouse to the Last Mile Center (again, different for different Warehouses), and a cost to ship a package from the Last Mile Center to the customer. In addition, there is a time element. It takes time to go from one Warehouse to another, and from a Warehouse to the Last Mile