Answer:
18,000 per year
Step-by-step explanation:
investment 72,000
payback in four year thus: the project pays itself in four year.
Also as the expected annual cash savings are equal between years
we con conclude:

72,000/ cash flow = 4
cash flow = 72,000 / 4 = 18,000
we are considering the cash savings adn depreciatin is not a monetary concept. We must ignore depreciation.