Estimate X from given Y in 4th order polynomial function

[LunaLouise]

Hello,

I have a 4th order polynomial data set for which I would like to estimate a x-value from a given y-value.

I've tried the methods in this thread and this thread, which both give me the same answer. Only the answer is not what I expected.

Obviously I'm doing something wrong or am using the wrong examples. Can someone please donate me some of their time and have a look? I've attached my worksheet.

I'd be very grateful.
Victoria

[LunaLouise]

I've not found an automated solution, but use Excel Solver manually to find a solution.

I'll do for now.

[arthurbr]

Thx for keeping us informed

[LunaLouise]

No problem! We all like a clean board.