13. A shell and tube heat exchanger is to be used in a corrosive service. If carbon steel tubes are used, the cost of the exchanger is estimated to be 160,000, and it is expected that the exchanger will need to be replaced after two years. If stainless steel tubes are used, the Economic Analysis 77 service life will be increased to ve years, but the cost increases to 400,000. If the cost of capital is 15%, which option should be selected