Solve this formula for r. Simplify your answer.

`E/d = (R + r)/r`

Make sure you use parentheses around any polynomials in the numerator and/or denominator.

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`E/d=(R+r)/r`

Now multiply whole expression by `dr.`

`Er=Rd+rd`

`Er-rd=Rd`

`r(E-d)=Rd`

Now divide whole expression by `(E-d).`

`r=(Rd)/(E-d)` **<-- Your solution.**

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