Formula to build net to gross calculation

Hi everyone,

Could you guide me on which formula is the correct one to use to do a net to gross calculation? I have the net and want to more easily calculate the gross up of it.
In the attached is what I used to build it gross to net, now trying to reverse it / do it the other way around, tried vlookup, what-if analysis, searched online but I'm doing smth wrong and not sure anymore if one formula could work at all.

It's a marginal tax rate and pension is deductible ie. Net salary = Gross salary - pension - income tax.

I guess I can do it if I know which are the correct formulas and logic.

Thanks a lot in advance!

See here for your TAX calculation

http://www.mcgimpsey.com/excel/variablerate.html