Answer
$ \left[\begin{array}{rr}
13 & -13\\
7 & 7\\
-7 & 14
\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.
---
$\left[\begin{array}{ll}
4 & -3\\
7 & 2\\
-6 & 8
\end{array}\right]+\left[\begin{array}{ll}
9 & -10\\
0 & 5\\
-1 & 6
\end{array}\right]=\qquad$ ... dimensions match, continue
$=\left[\begin{array}{ll}
4+9 & -3+(-10)\\
7+0 & 2+5\\
-6+(-1) & 8+6
\end{array}\right]$
$=\left[\begin{array}{rr}
13 & -13\\
7 & 7\\
-7 & 14
\end{array}\right]$
