Chapter 1 - Section 1.2 - Formulas and Percent - 1.2 Exercises - Page 61: 6

$t=\dfrac{d}{r}$

Using the properties of equality, in terms of $ t ,$ the given formula, $ d=rt ,$ is equivalent to \begin{array}{l}\require{cancel} \dfrac{d}{r}=\dfrac{rt}{r} \\\\ \dfrac{d}{r}=t \\\\ t=\dfrac{d}{r} .\end{array}