Sejam as matrizes $A=\left[\begin{array}{ccc}1& -1& 1\\ 2& 1& -3\\ 1& 1& -1\end{array}\right],B=\left[\begin{array}{c}x\\ y\\ z\end{array}\right]$ e $C=\left[\begin{array}{c}0\\ -12\\ -4\end{array}\right]$.Se $AB=C$, então $x+y+z$ é igual a