The compressor unit of REL Refineries needs about on an average of 816 cases of SAE 30 weight oil every year. The ordering costs are $12, carrying costs are $4 per case per year. The maintainance manager Mrs. Kiran Shah is looking at a new price schedule by the supplier Indane Oil that indicates orders less than 50 cases will cost $20 per case, 50 to 70 cases will cost $18 per case, 80 to 90 cases will cost $17 per case and larger orders will cost $16 per case. Determine the optimum order quantity and the total cost Mrs. Shah should Order.