9. If variables $x, y$ satisfy the conditions $\left\{ \begin{array}{c} 3x - y \leq 0 \\ x - 3y + 5 \geq 0 \end{array} \right.$, then the maximum value of $z = x + y$ is $\_\_\_\_$
6 \leq x - y \le
9. If variables $x, y$ satisfy the conditions $\left\{ \begin{array}{c} 3x - y \leq 0 \\ x - 3y + 5 \geq 0 \end{array} \right.$, then the maximum value of $z = x + y$ is $\_\_\_\_$\\