A piece of equipment has a first cost of $160,000, a maximum useful life of 7 years, and a market (salvage) value described by the relation S=120,0009,000k, where k is the number of years since it was purchased. The salvage value cannot go below zero. The AOC series is estimated using AOC=60,000+6,000K. The interest rate is 9% per year. Determine the economic service life and the respective AW. The economic service life is year(s) and the AW value is $