The Gooey Glue Co. production manager purchased a stainless steel mixing tank at auction for $15,000. Because it was a good deal, she estimates the tank can be sold at any time for the purchase price of $15,000, even if the mixer machinery isn’t working. The machinery needs $2000 in repairs now and is expected to cost $500 during the next year to operate. It seems likely that this cost will increase by another $500 ever year for the next few years. What is the optimum economic service life that can be used in a replacement analysis based on a 15% per year MARR?