Answer
$ \left[\begin{array}{r}
4\\
-5\\
4
\end{array}\right]$
Work Step by Step
1. Check if the matrices have the same dimension. If they don't, the sum/difference is not defined.
2. The sum/difference will be a matrix with the same dimension.
3. Position by position, add/subtract the corresponding entries.
---
$\left[\begin{array}{l}
12\\
-1\\
3
\end{array}\right]-\left[\begin{array}{l}
8\\
4\\
-1
\end{array}\right]=\qquad$ ... dimensions match, continue
$=\left[\begin{array}{l}
12-8\\
-1-4\\
3-(-1)
\end{array}\right]$
$=\left[\begin{array}{r}
4\\
-5\\
4
\end{array}\right]$
