In a periodic (P) review system, the lead time for a box of weed-killer is three weeks and the review period is two (i.e., an order is placed every other week). Demand during the protection interval averages 320 boxes, with a standard deviation of 80 boxes. a. What is the average weekly demand? b. If the target inventory level is set at 500 units, what is the safety stock? What is the cycle-service level?