How do you calculate a) the NPV with an OCC of 10% / moderate risk and b) the IRR (assuming NPV > 0) for the following, as I am struggling, even using excel? Any help would be appreciated.

Here is the data (month and net positive cash flow values) I am using in my calculations (note that up to month 20 the cash flows are negative, but the sum of all the cash flows is positive: 1342). The OCC for my industry is about 10% for moderate risk.

Month 1 -£173 Month 2 -£24 Month 3 -£1374 Month 4 -£45 Month 5 -£97 Month 6 -£31 Month 7 -£31 Month 8 -£31 Month 9 -£31 Month 10 -£82 Month 11 -£141 Month 12 -£200 Month 13 -£259 Month 14 -£319 Month 15 -£321 Month 16 -£322 Month 17 -£323 Month 18 -£324 Month 19 -£326 Month 20 -£327 Month 21 £380 Month 22 £383 Month 23 £1221 Month 24 £1324 Month 25 £1427 Month 26 £941 Month 27 £449