A city water and waste-water department has a four-year-old sludge pump that was initially purchased for $65,000. This pump can be kept in service for an additional four years, or it can be sold for $36,000 and replaced by a new pump. The purchase price of the replacement pump is 52,000. The projected MVs and operating and maintenance costs over the four-year planning horizon are shown in the table that follows. Assuming the MARR is 9%, (a) determine the economic life of the challenger and (b) determine when the defender should be replaced. Challenger Defender MV at EOY MV at EOY O&M Costs O&M Costs Year $35.000 27,500 20,000 12,500 $12000 $23,500 20,500 17,500 14,500 $19,500 22,000 14,500 17,000 19,500 2 24.500 27,000 Click the icon to view the interest and annuity table for discrete compounding when the MARR is 9% per year. a. The economic life of the challenger isyear(s). (Round to the nearest whole number.) b. The defender should be replaced