Answer
$t=\dfrac{A-P}{Pr}$
Work Step by Step
Distribute $P$ to obtain:
$A=P+Prt$
Subtract $P$ on both sides to obtain:
$A-P=Prt$
Divide $Pr$ on both sides to obtain:
$\dfrac{A-P}{Pr} = \dfrac{Prt}{Pr}$
Cancel the common factors to obtain:
$\require{cancel}
\dfrac{A-P}{Pr} = \dfrac{\cancel{Pr}t}{\cancel{P r}}
\\\dfrac{A-P}{Pr} = t$
