Answer
$I=\dfrac{E}{R+r}$
Work Step by Step
Factor out $I$ on the left side to find:
$I(R+r)=E$
Divide by $R+r$ on both sides to find:
$\dfrac{I(R+r)}{R+r} = \dfrac{E}{R+r}
\\I=\dfrac{E}{R+r}$
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