A company has sufficient cash reserves to replace a milling machine. The current market value of the old machine is 70,000 and will be 50,000, 40,000, 30,000, 15,000, and 0 at the end of each of the next five years as it approaches the end of its service life. The annual maintenance costs are estimated to increase with each year from 9000, 11,000, 14,000, 15000 to 16,500. How much longer should the milling machine be kept, if MARR is 10%?