Step 1:
First, we multiply the first two matrices:
$\left(\begin{array}{lll}2 & 2 & x\end{array}\right)\left(\begin{array}{lll}1 & 2 & 3 \\ 0 & 1 & 5 \\ 0 & 2 & 1\end{array}\right) = \left(\begin{array}{lll}2 & 6+2x & 16+x\end{array}\right)$
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