Assume in analyzing alternative proposals that Proposal F has a useful life of six years and Proposal J has a useful life of nine years. What is one widely used method to make the net present values of the proposals comparable? a. Adjust the life of Proposal J to a time period that is equal to that of Proposal F by estimating a residual value at the end of Year 6. b. Ignore the fact that Proposal F has a useful life of six years and treat it as if it has a useful life of nine years. c. Ignore the useful lives of six and nine years and compute the average rate of return. d. Ignore the useful lives of six and nine years and find an average (7 1/2 years).