Answer
$ \left[\begin{array}{ll}
0 & 0\\
0 & 0
\end{array}\right]$
Work Step by Step
All the matrices are 2$\times$2.
The sums and differences are 2$\times$2 matrices,
The product of two 2$\times$2 matrices is a 2$\times$2 matrix.
$A-B=\left[\begin{array}{ll}
1-1 & 0-0\\
0-0 & 1-(-1)
\end{array}\right]=\left[\begin{array}{ll}
0 & 0\\
0 & 2
\end{array}\right]$
$C+D=\left[\begin{array}{ll}
-1+(-1) & 0+0\\
0+0 & 1+(-1)
\end{array}\right]=\left[\begin{array}{ll}
-2 & 0\\
0 & 0
\end{array}\right]$
$(A-B)(C+D)=\left[\begin{array}{ll}
0 & 0\\
0 & 2
\end{array}\right]\left[\begin{array}{ll}
-2 & 0\\
0 & 0
\end{array}\right]$
$=\left[\begin{array}{ll}
0+0 & 0+0\\
0+0 & 0+0
\end{array}\right]$
$=\left[\begin{array}{ll}
0 & 0\\
0 & 0
\end{array}\right]$
