Can someone help me reverse this formula in google sheets? I really don't understand what i'm doing and I need help

https://docs.google.com/spreadsheets/d/199UF6crJNo7Kh_1oWEjB_oCHIz7ZCPVlV0Oz1fu90Ow/edit?usp=sharing

I have a formula where you input base stat and level and it's converted to the final stat for a pokemon-type game, but I'm trying to reverse it so i input the final stat and the level and it gets converted to the base stat. Any help or explanation is greatly appreciated as i'm really lost.

=ROUNDDOWN(((2 * C2 * J2 / 100) + 5) + (31 * (J2 / 100))) where C2 is base stat and j2 is level
=ROUNDDOWN(((2 * B2 * J2 / 100) + J2 + 10) + (31 * (J2 / 100))) where B2 is base stat and j2 is level would also be greatly appreciated