Answer
$ \left[\begin{array}{rr}
-2 & -5\\
17 & 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.
---
$\left[\begin{array}{ll}
-4 & 3\\
12 & -6
\end{array}\right]+\left[\begin{array}{ll}
2 & -8\\
5 & 10
\end{array}\right]=\qquad$ ... dimensions match, continue
$=\left[\begin{array}{ll}
-4+2 & 3+(-8)\\
12+5 & -6+10
\end{array}\right]$
$=\left[\begin{array}{rr}
-2 & -5\\
17 & 4
\end{array}\right]$
