Kindly please answer this question and show the step by step working . Thank you very much :)

4. Potable water is in short supply in many countries. To address this need, two mutually exclusive water purification systems are being considered for implementation in China. Doing nothing is not an option. Refer to the data below and state your key assumptions in working this problem. a. Use the PW method to determine which system should be selected when MARR =8% per year. b. Which system should be selected when MARR=15% per year