Units are the cheat code to every physics/chemistry test. Once you know the units of your "known" you can usually derive almost any equation from simple logic. At a minimum it will get you close enough that you can remember the rest if you studied at least a little bit.

I just walked an organic chemistry student through hat on a fairly tough problem. Just showed them how every unit for every known can infer an equation, and all those equations for all your known will either get you to a complete system of equations to derive your needed formula, or will at least get you most of the way there and you can fill in the rest with a bit of logic).

It worked, we were trying to calculate morality for an acid when only the percentage by weight is given
.