Question: Write the matrix equation as a system of equations and solve the system.

\[\left[ \begin{matrix} 1 & 2 & 3 \\ 1 & 1 & 1 \\ -1 & 1 & 2 \\ \end{matrix} \right]\left[ \begin{matrix} x \\ y \\ z \\ \end{matrix} \right]=\left[ \begin{matrix} 1 \\ 12 \\ 2 \\ \end{matrix} \right]\]