21. Assume you are facing two mutually exclusive projects F and S, and their cash flows are listed as below (21) a. What are the payback periods for F and S respectively? (6) b. What are the NPVs for F and S respectively given a discount rate of 15% ? (4) c. What are the profitability index for F and S respectively? (4) d. What are the IRRs for F and S respectively? (4) e. Do you obtain any different decisions from b and d ? Explain why if you do (3)