8.39 Your dad made the following estimates as he con- 51** sidered upgrading the air-conditioning system in their home. Use AW analysis to determine the sen- sitivity of the economic decision to interest rates of 4%, 6%, and 8% per year. Work this problem by (a) factors, and (b) spreadsheet. System 1 2 -10,000 -600 First cost, $ Annual operating cost, $ Salvage (disposal) value, $ New compressor and motor cost at midlife, $ -17,000 -150 -300 -100 -1,750 Life, years -3,000 12 8