Chapter 1 - Section 1.2 - Formulas and Percent - 1.2 Exercises - Page 62: 21

$t=\dfrac{A-P}{Pr}$

Using the properties of equality, in terms of $ t ,$ the given formula, $ A=P(1+rt) ,$ is equivalent to \begin{array}{l}\require{cancel} A=P+Prt \\\\ A-P=Prt \\\\ \dfrac{A-P}{Pr}=t \\\\ t=\dfrac{A-P}{Pr} .\end{array}