Answer
$r=\frac{E-IR}{I}$
Work Step by Step
We are given that $E=I(r+r)$. We can use the distributive property to multiply out the terms on the right side.
$E=I\times(r+r)=Ir+IR$
Subtract IR from both sides.
$E-IR=Ir$
Divide both sides by I.
$r=\frac{E-IR}{I}$
