Which statement defines externality?

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