6. 8.39 Your dad made the following estimates as he considered upgrading the air-conditioning system in their home. Use AW analysis to determine the sensitivity of the economic decision to interest rates of 4%, 6%, and 8% per year. Work this problem by

(a) factors, and

(b) spreadsheet. Table Summary: Table divided into two columns compares cost of installing an air-conditioning system based on the interest rate and life span. The column headers are marked from left to right as: system; 1; and 2. System 1 2 First cost, $ −10,000 −17,000 Annual operating cost, $ −600 −150 Salvage (disposal) value, $ −100 −300 New compressor and motor cost at midlife, $ −1,750 −3,000 System 1 2 Life, years 8 12