A small business has a tire remover and remover machine. Buying a new machine involves investing $ 25,000. It assumes that the business started in 2021 with a new machine, and since the investment has already been made, it is considered a sunk cost, irrelevant for subsequent decisions.

The table shows the salvage value values if the machine is sold used, and the operating costs for the 4 years the machine is planned to be used. At the end of the 4 years, this machine will no longer be needed:

Age	Salvage Value	Cost of operation
1	15000	1000
2	10000	3000
3	8000	5000
4	6000	7000

You want to make a replacement plan for the machine, indicating whether at the end of each year it is convenient to sell the machine or keep it.

Apply dynamic programming to solve the problem. Submit your solution in a spreadsheet.