Answer
$$ \frac{y-b}{x}, \ \ -2$$
Work Step by Step
To solve the given equation for $m$, we move out the term $b$ and then divide both sides by $x$ as follows
$$
y=mx+b\Longrightarrow mx=y-b \Longrightarrow m=\frac{y-b}{x}
.$$
Now, by substitution, we have
$$
m=\frac{y-b}{x}=\frac{2-9}{3}=-2.33\approx -2
.$$
