Solve this system of equations.
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What is a solution to this system of equations:
$\left\{\begin{matrix} x+2y-z=6\\ 2x+y+z=9\\ 3x+4y+z=18\end{matrix}\right.$
$\left\{\begin{matrix} x=3\\ y=-2\\ z=-1\end{matrix}\right.$
$\left\{\begin{matrix} x=3\\ y=2\\ z=1\end{matrix}\right.$
$\left\{\begin{matrix} x=-3\\ y=2\\ z=-1\end{matrix}\right.$
$\left\{\begin{matrix} x=3\\ y=-2\\ z=1\end{matrix}\right.$
$\left\{\begin{matrix} x=-3\\ y=2\\ z=1\end{matrix}\right.$
