I have a question of how to make a geometric interpretation of this problem
\begin{eqnarray} \mbox{max} & z = 3x_1+x_3 \\ s.a: & \\ & \begin{array}{cc} x_1+2x_2+x_3+x_4& =10 \\ x_1-2x_2+2x_3&=6\\ 1 \leq x_1\leq 4&\\ -5 \leq x_2 \leq 4\\ 0 \leq x_3 \leq 4&\\ 0 \leq x_4 \leq 5& \end{array} \end{eqnarray}