Question 1: ILP Maintenance Scheduling (10 marks) The service manager for the Greyhound Bus Company is concerned with the backlog of bus. engines needing repair that has accumulated in the past week. The repair facility uses a single maintenance crew to disassemble, overhaul, and reassemble each engine. At the moment, five engines are waiting for overhaul, and the maintenance crew is ready for its next assignment. Estimated overhaul times are given below:

Engine #	1	2	3	4	5
Repair Time	22	16	35	12	28

The service managers performance is judged, in part, on the average time an engine spends in the shop awaiting or receiving an overhaul. He would like to determine the best order in which to process the engines so as to minimize the average time spent in the shop.

a. Provide an appropriate formulation.