For many routine maintenance replacement items, a hotel manager has a choice between doing all of the maintenance at once (such as changing air filters in all guest rooms quarterly) and doing it as needed (such as replacing hot water heater pumps when they stop working). In other cases, such as replacing parking lot light bulbs or fan belts on motors, the manager has a choice between systematic total replacement and a "replace as needed" approach. Assume that you were required to decide on a replacement program for exterior parking lot lights in a hotel with parking for 150 cars. What factors would influence your decision?