please solve by hand, on paper.

Problem 7: A special-purpose machine is to be purchased at a cost of $30,000. The follow- ing table shows the expected annual operating and maintenance cost and the salvage value for each year of service: Year of Service O&M Cont Market Value 1 $5,000 $25,800 2 $6,500 $16,000 3 $10,000 $10,000 4 $12,500 $5,000 5 $14,800 $0 If the interest rate is 12%, what is the economic service life for this machine