Consider the following linear programming problem:

MinZ$=$

$6x_1+4x_2$

Subject to:

$4x_1+2x_{2}100$

$2x_1+3x_{2}90$

$x_1,x_{2}0$

What is the lower limit of the right$-$hand side of the second constraint $(q_2)?$

$30$

$40$

$50$