I solved the following matrix
$\begin{bmatrix}1 & 2 & -1 & | & 3\\2 & 4 & -2 & | & 6\\3 & 6 & 2 & | & -1\end{bmatrix}$
and got
$\begin{bmatrix}1 & 2 & 0 & | & 1\\0 & 0 & 1 & | & -2\\0 & 0 & 0 & | & 0\end{bmatrix}$
therefore my final answer would be:
x =1 - 2y
z = -2
how do I write the "y" part?
The solution is correct as is, but a better way to present it would be:
$x=1-2t$
$y=t$
$z=-2$
where $t\in\mathbb R$.