A maintenance department of a large hospital uses about 816 cases of liquidcleanser annually. Ordering costs are $12, carrying costs are $4 per unit per yearand the new price schedule indicates that orders of less than 50 cases will cost$20 per case, 50 to 79 cases will cost $18 per case, 80 to 99 cases will cost $17per case and larger orders will cost $16 per case. What is the best purchasequantity; explain why?