Jasper’s Grocery places an order for Monster every 3 weeks. Once the order is placed, delivery to the store typically occurs in 1 week. Average demand is 100 cases per week and the standard deviation of demand is 20 cases / week. The store policy is to stock an amount of inventory which allows for an average stockout condition of 10% while waiting for replenishment. It is time to place an order and there are 420 cases on hand. How many units should be ordered?