College Algebra, Chapter 1, 1.2, Section 1.2, Problem 6

Find formulas for $r$ and $t$, suppose that $d = rt$.

if $d = rt$, then


$
\begin{array}{cccccc}
\text{if} & d = rt, & \text{then} & \text{if} & d = rt, & \text{then} \\
& d = rt & \text{divide $t$ on both sides of the equation } & & d = rt & \text{divide $r$ on both sides} \\
& \displaystyle \frac{d}{dt} = \frac{r \cancel{t}}{\cancel{t}} & \text{solve for } r & & \displaystyle \frac{d}{r} = \frac{\cancel{r} t}{\cancel{r}} & \text{solve for } t \\
& \displaystyle r = \frac{d}{y} & & & \displaystyle t = \frac{d}{r} &
\end{array}
$