A = p + prt
The above equation can be solved for “r” in such a way.
Subtract “p” from both sides;
A – p = p + prt – p
A – p = prt
Divide both sides by “p” and “t”;
A/pt – p/pt = prt/pt
A/pt – 1/t = r
Or
r = A/pt – 1/t
