Answer
$ \left[\begin{array}{rr}
-6 & 8\\
4 & 2
\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.
---
$\left[\begin{array}{ll}
-6 & 8\\
0 & 0
\end{array}\right]-\left[\begin{array}{ll}
0 & 0\\
-4 & -2
\end{array}\right]=\qquad$ ... dimensions match, continue
$=\left[\begin{array}{ll}
-6-0 & 8-0\\
0-(-4) & 0-(-2)
\end{array}\right]$
$=\left[\begin{array}{rr}
-6 & 8\\
4 & 2
\end{array}\right]$
