## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

$x=\dfrac{S}{r+s}$
Using the properties of equality, in terms of $x$, the given equation, $S=rx+sx$, is equivalent to \begin{array}{l} S=x(r+s) \\\\ \dfrac{S}{r+s}=x \\\\ x=\dfrac{S}{r+s} .\end{array}