## Elementary Technical Mathematics

$y= \frac{x}{3}-3$
By subtracting $x$ from each side and then dividing each side by $-3$, we get: $$x-3y=9\Longrightarrow -3y=9-x \\ \Longrightarrow y=-\frac{9-x}{3}=\frac{x}{3}-3 .$$