NEHBY – payback period

Hi. I am struggling to calculate the payback period for NEHBY question (past ACCA exam paper).

Through cumulative net cash flow I have got the payback period to 5 but cannot work out how many months?

Initial investment Net cash flows Discount factor Present value

Year 0 (5) 1 (5)
Year 1 (0·5) 0·926 (0·463)
Year 2 0·5 0·857 0·4285
Year 3 1 0·794 0·794
Year 4 1·5 0·735 1·1025
Year 5 2 0·681 1·362
Year 6 2 0·630 1·26
Year 7 2 0·583 1·166
––––––
NPV 0·65

Thank you!!