I really need help answering these questions for economics

The manager of the quick stop corner convenience store (which never closes) sells four cases of stein beer each day. order costs are $8.00 per order, and stein beer costs $.80 per six-pack (each case of stein beer contains four six-packs). orders arrive three days from the time they are placed. daily holding costs are equal to 5 percent of the cost of the beer. if he were to order 16 cases of stein beer at a time, what would be the average inventory level? a. 0.25 days b. 3 days c. 1 day d. 4 days e. 20 days