An engineer has been offered an investment opportunity that will require a cash outlay of $40,000 now for a cash inflow of $3500 for each year of investment. However, she must state not that number of years she plans to retain the investment. Additionally, if the investment is retained for 6 years, a lump-sum amount of $36,000 will be returned to her; after 10 years, the lump-sum return is anticipated to be $49,000, and after 15 years, it is estimated to be $55,000. Money is currently worth 10% per year. (a) Is the decision sensitive to the retention period? If so, what investment period is best? (b) Write the format of the spreadsheet function that will display the correct PW values.