I wonder if the calculation PV of cash flow on the answer has rounding issues. I have the same net cash flow figures as on the answer, but with DF @11%, only year 1 figure is the same as the answer, the remaining are different, I got NPV -1000 rather than -6000. will rounding issue have impact on gaining full mark?
However the difference in your answer seems a lot for it just to be due to rounding. Have you checked all the individual cash flows in your answer (because the marks are for each of the cash flows separately rather than for the final NPV)?