Refer to Example 9-4. By how much would the MARR have to change before the economic life

Question:

Refer to Example 9-4. By how much would the have to change before the economic life decreases by one year? How about to increase the economic life by one year?
MARR
Minimum Acceptable Rate of Return (MARR), or hurdle rate is the minimum rate of return on a project a manager or company is willing to accept before starting a project, given its risk and the opportunity cost of forgoing other...