Formula For Annuity Cost Basis Calculating A 'change In Maintenance Cost' Per Annum Using Annuity?

Calculating a 'change in maintenance cost' per annum using annuity? - formula for annuity cost basis

The question is:

What would the cost of annual maintenance contract?

The information we have is that the maintenance costs of £ 8,000 per year at present. I need the formula to solve this problem:

Changes in maintenance costs --
X * annuity factor = change in NPV

My shift the NAV is £ 431,868.20

I have a solution, but I have no idea where the annuity to get? Expect nothing. Thank you.