13. A mail-order house uses 18,000 boxes a year. Carrying costs are 60 cents per box a year, and ordering costs are $96. The following price schedule applies. Determine the following: a. The optimal order quantity b. The number of orders per year Number of Boxes 1,000 to 1,999 2,000 to 4,999 5,000 to 9,999 10,000 or more Price per Box $1.25 1.20 1.15 1.10