A company manufactures hair dryers. Demand for hair dryer is at the rate of 100 units per month and holding cost is at the rate of $0.50 per week. If the shortage cost is at the rate of $4.00 per month and ordering cost is $80 per order, find:

a. Optimal order quantity

b. Maximum inventory level

c. Portion of time shortages on hand

d. Total cost.