Trouble with a calculation formula using %…

I’ve been asked to update a calculator by a client.

This calculator here: https://www.timesharecompensation.co.uk/compensation-calculator-internal/

My current (unmodified) formula is this..
(2*(fieldname9+fieldname11))+ (fieldname12*fieldname5)

The client has asked me to modify my current formula so that 5% is added to the ‘Average Maintainence fees’-(fieldname12) for each year displayed in ‘Years owned’-(fieldname5).

So please ignore the first 2 fields in the form for this.

E.g. if the Average Fees were ￡100.00 it would look something like this…
1 Year: 105.00
2 Years: 215.25
3 Years: 331.01
4 Years: 452.56
5 Years: 580.19

Any idea what formula I could use to get this to work?

I’ve been given a spreadsheet by them to demonstrate, but the issue is I can’t copy the calculation they’ve used as it relies on data that is present in the spreadsheet, whereas this form will need to calculate it all at once.. so i’m a little confused.

Any help is much appreciated!