Answer
$ r=\dfrac{A-P}{Pt}$
Work Step by Step
Use distributive property on the right side.
$A=P+Prt$
Subtract $P$ from both sides.
$A-P=P+Prt-P$
Simplify.
$A-P=Prt$
Divide both sides by $Pt$.
$\dfrac{A-P}{Pt}=\dfrac{Prt}{Pt}$
Simplify.
$\dfrac{A-P}{Pt}=r$
