if it is kept ( po 2015. The present worth of the after-tax cash flows through year k, PW, for a defender 13- year remaining useful life) and a challenger (5-year useful life) are as follows: PW of ATCF through year k, PW Year Defender Challenger -$14,020 -28,100 -43.075 -$18,630 -34,575 -48,130 -65,320 -77.910 Assume the after-tax MARR is 12% per year. Based on this information, answer the following: a. What is the economic life and the related minimum equivalent uniform annual cost, EVAC, when k = N* Ar for both the defender and the challenger? b. When should the challenger (based on the present analysis) replace the defender? Why? 6. What assumption(s) have you made in answering Part (b)