Step 1:
First, we notice that the given matrix $M$ is a block matrix, which can be written as follows:
$$M = \left[\begin{array}{cc}
A & B \\
0 & C
\end{array}\right]$$
where $A = \left[\begin{array}{cc}
1 & 2 \\
8 & 7
\end{array}\right]$, $B =
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