For equipment that has a first cost of $17,500, the estimated operating costs and year-end salvage values are as shown. Year Operating Cost, $ Salvage Value, $ 1 -1,000 7,000 2 -1,200 5,000 3 -1,300 4,500 4 -2,000 3,000 5 -3,000 2,000 Determine the economic service life ESL, at /-10% per year using factors. The economic service life ESL, is | years with the AW = $-