Difficulty answering an augmented matrices question

Question

How would I express these equations as an augmented matrix? I know how to convert simply equations to an augmented matrix but the added $k$ and $z$ are confusing me.

$x + 2y - z = -3$

$3x + 5y + kz = -4$

$9x + (k+13)y + 6z = 9$

Answer 1

$k$ may be just a constant.

You can write it as,

$\begin{bmatrix}1 & 2 & -1 \\ 3 & 5 & k \\9 & k+13&6\end{bmatrix}\begin{bmatrix}x\\y\\z\end{bmatrix}=\begin{bmatrix}-3\\-4\\9\end{bmatrix}$