6-18. A stem cell research project requires expensive specialized laboratory equipment. For this purpose, three pieces of equipment and their associated cash flows (listed below) are under consideration. One piece of equipment must be selected, and the laboratory's MARR is 15% per year. (64) EOY A 0$136,500-$84,000-$126,000 1-4 $12,500 -$28,500 -$15,500 5 $10,000-$28,500-$15,500 a. Use the PW method to rank-order the economic attractiveness of the three projects. b. Determine the interest rate at which the laboratory would be indifferent between Equipment B and Equipment C