Logic behind Justified P/S, P/B, P/E

CFA Level II Equities
#1

Do any of you have shorthand ways to remember the formulas for Justified P/S, P/B, P/E? I’m having trouble recalling them but if you have some logic that I can simply derive in my head and come up with the formulas, it’d be tremendously helpful.

#2

Also, if you have any logical tricks to get to their Forward looking counterparts, that’d be great too.