The Board of Directors of NMN Ltd, a manufacturing company, is examining whether to purchase a new machine for 500,000 payable immediately, with a useful economic life of 8 years. The expected net cash inflows from the use of the machine are 80,000 per year. The Pay Back period of the machine is: O a. 6 years and 3 months O b. 4 years and 4 months O c. None of the others O d. 7 years O e. 2 years and 6 months