Please I need guidelines or resources for solving a linear Programming problem which has negative constraints
min $ z = 2x_1 - 6x_2-x_3$
s.t
$ 3x_1 + x_2 + 4x_3\le 6$
$-x_1 + x_2 - 6x_3 \ge -6$
$-x_1 + 3x_2 - x_3 \le 9 $
here is my problem $x_1\le -2 , x_2 \ge -3$
how do I change this to get non negative constraints.