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 now for $29,500 and replaced by a new pump. The purchase price of the replacement pump is $46,000. 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 10\%, (a) determine the economic lte of the challenger and (b) determine when the detender should be replaced. Click the icon to view the interest and annuity table for discrete compounding when the MARR is 10% per year. a. The economic life of the chalenger is yoar(s). (Round to the nearest whole number.) b. The defender should be A. kept for at least one more year B. replaced now