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.
$A+B=\left[\begin{array}{ll}
1+1 & 0+0\\
0+0 & 1+(-1)
\end{array}\right]=\left[\begin{array}{ll}
2 & 0\\
0 & 0
\end{array}\right]$
$C-D=\left[\begin{array}{ll}
-1-(-1) & 0-0\\
0-0 & 1-(-1)
\end{array}\right]=\left[\begin{array}{ll}
0 & 0\\
0 & 2
\end{array}\right]$
$(A+B)(C-D)=\left[\begin{array}{ll}
2 & 0\\
0 & 0
\end{array}\right]\left[\begin{array}{ll}
0 & 0\\
0 & 2
\end{array}\right]=\left[\begin{array}{ll}
0+0 & 0+0\\
0+0 & 0+0
\end{array}\right]$
$=\left[\begin{array}{ll}
0 & 0\\
0 & 0
\end{array}\right]$