dicide both sides by P:

A/P=1+rt.

Subtract 1 form both sides (as two things that are equal are still equal when

the same thing is added or subracted from both)

A/P - 1 =rt

Divide both sides bt t:

(A/P - 1)/t =r,

or:

r = (A/P - 1)/t,

z= x + yrSolve x + yr = z for z

(if something is equal to a thing, then the thing is equal to that something)

RonL