Answer
\begin{align*}
\text{Slope: }&m=-\dfrac{1}{2}
\\y-\text{intercept: }& -6
\end{align*}
Work Step by Step
In the form $y=mx+b,$ the given equation, $
-x-2y=12
,$ is equivalent to
\begin{align*}
-x+x-2y&=x+12
\\
-2y&=x+12
\\\\
\dfrac{-2y}{-2}&=\dfrac{x+12}{-2}
\\\\
y&=\dfrac{1}{-2}x+\dfrac{12}{-2}
\\\\
y&=-\dfrac{1}{2}x-6
.\end{align*}
The Slope-Intercept Form of the equation of lines, which is given by $y=mx+b,$ has slope $m$ and $y$-intercept of $b$. With the equation above then
\begin{align*}
\text{Slope: }&m=-\dfrac{1}{2}
\\y-\text{intercept: }& -6
.\end{align*}
