please help me answer the questions based on the work sheet

Project Cash Flow RANK NPV RANK PB RANK PI 1 3,310 5 73.09 6 7 5 3.65% 2 2,165 8 -85.45 8 2 2 -4.27% RANK IRR 6 10.87% 8 6.31% RANK 6 8 3 10,000 1 393.92 1 15 8 19.70 % 1 11.33 % 1 4 3,561 4 228.22 2 6 4 9.21% 5 4,200 2 129.70 5 8 7 6.49% 6 2,200 7 0 7 1 1 0% 7 2,560 6 165.04 4 2 2 8.25% 2 12.33 % 3 5 11.12% 7 10% 5 7 3 15.26 % 2 8 4,150 3 259.96 3 7 5 10.98 % 4 11.96 % 4 Which of the two projects, 7 or 8, is more attarctive? How sensitive is our ranking to the use of high discount rates? What rank shoul we assign to each project? Why do payback and NPV not agree completely? Why do average return on investment and NPV not agree completely? Which criterion is best? Are these projects comparable on the basis of NPV