Answer
$\color{blue}{y=\dfrac{C-Ax}{B}}$
Work Step by Step
Subtract $Ax$ to both sides of the equation:
$Ax+By-Ax=C-Ax
\\By=C-Ax$
Divide $B$ to both sides of the equation:
$\dfrac{By}{B}=\dfrac{C-Ax}{B}
\\\color{blue}{y=\dfrac{C-Ax}{B}}$