6-18. A solar energy research center requires special- ized research equipment. For this purpose, four pieces of equipment and their associated cash flows (listed below) are under consideration. One piece of equip- ment must be selected and the laboratory's MARR is 10% per year. (64) Equipment EOY 2 4 -$150,000-$80,000-$125,000-$100,000 1-3 -$20,000 -$30,000 -$25,000 -$40,000 4 $30,000 -$30,000$25,000-$45,000 5 -$40,000 -$35,000 $30,000-$50,000 a. Use the PW method to rank-order the economic attractiveness of the four pieces of equipment. b. Determine the interest rate at which the laboratory would be indifferent between Equipments 2 and 3