## Introductory Algebra for College Students (7th Edition)

$$r = \frac{S - P}{Pt}$$
To solve the equation for $r$, we must isolate $r$. We first subtract $P$ from each side: $$S - P = Prt$$ We can then divide by both $P$ and $t$ together to get: $$r = \frac{S - P}{Pt}$$