19. A city water and wastewater depaltment has a four year old sludge pump that was initially purchased for SA. This pump can be kept in service for an additional four years, or it can be sold for SB and replaced by a new pump. The purchase price of the replacement pump is SC. The projected market values and operating and maintenance costs over four year planning horizon are shown in the table that follows. Assuming the MARR is D% a) (4 points) detennine the economic life of the defender and the annual cost of defender in its economic life b) (4 points) detennine the economic life of the challenger and the annual cost of challenger in its economic life c) (3 points) detennine when the defender should be replaced. Year Defender MV at end of Operation & Challen er M V at end of Operation & year maintenance costs year maintenance costs