Phenomenal! This is a solid prototype, clean execution. I've had exactly this idea, too: I've already given the spreadsheet the relationships between these values, why can't it just work backwards when values change? That premise hides a ton of complexity, though, I'm sure. Lots of scary matrices.

Thanks! Yes I loved the ratio of apparent simplicity to underlying complexity of this project. I have filled around 120 pages of draft and notes just for the math of the solver :)