4. Suppose that you are the manager of a production department that uses 400 boxes of rivets per year. The supplier quotes you a price of $8.50 per box for an order size of 199 boxes or less, a price of $8.00 per box for orders of 200 to 999 boxes, and a price of $7.50 per box for an order of 1,000 or more boxes. You assign a holding cost of 20 percent of the price to this inventory. Assume ordering cost is $80/order. What order quantity would you use to minimize the total annual costs and what is the number of orders per year?