Answer
$x=\dfrac{a+b}{c}$
Work Step by Step
Multiply $x$ to both sides of the equation to obtain:
$\begin{array}{ccc}
\require{cancel}
&x\left(\dfrac{a}{x} + \dfrac{b}{x}\right)&=&c(x)
\\&\cancel{x}\left(\dfrac{a}{\cancel{x}}\right) + \cancel{x}\left(\dfrac{b}{\cancel{x}}\right)&=&cx
\\&a+b&=&cx
\end{array}$
Divide $c$ to both sides of the equation to obtain:
$\dfrac{a+b}{c} =x$
