[![enter image description here](https://i.stack.imgur.com/32gmi.png)](https://i.stack.imgur.com/32gmi.png)

I've been trying to solve this and I'm not getting anywhere. The k is really throwing me off. I row reduce and I get down to: \begin{bmatrix}6&0&14\\0&1&-1\\0&0&-7+k\end{bmatrix}

I'm a bit (a lot) lost.