The present worth of the cash ows through year k, Pwk, for a defender (three-year remaining useful life) and a challenger {five-year useful life) are given in the following table: PW of cash ows through year k, Pwk Year Defender Challenger 1 49620 -'| 5040 2 -2?'| 00 35575 3 12015 48150 4 -64000 5 -3?9'| 0 Please answer the following questions and attach your handwritten solutions in the next part. Assume that MARR is 10% per year. a) What is the economic service life for both the defender and the challenger, interpret the result based on the ESLs? b) When should we replace the defender if we use a xed Him planning horizon? Please upload your handwritten answers for both parts here