Answer
$$r=\frac{s}{B-1};\quad \:B\ne \:1$$
Work Step by Step
Solving the equation by isolating the variable using the rules of Algebra, we find:
$$ Br=r+s\\ Br-r=s\\ r\left(B-1\right)=s\\ r=\frac{s}{B-1};\quad \:B\ne \:1$$
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