A special purpose machine is to be purchased at a cost of $15,000. The following table shows the expected annual operating and maintenance cost and the salvage values for each year of service.

Year of Service	O&M Costs	Market Value
1	$2,500	$12,000
2	3,200	8,100
3	5,300	5,200
4	6,500	3,500
5	7,800	0

a) If the interest rate is 10%, what is the economic service life for this machine?

b) Repeat (a) above using i=15%.