Consider the following linear programming problem:

Max,$Z=120x_1+100x_2$

Subject to: $3x_1+4x_{2}8$

$($constraint $1)$

$10x_1+9x_{2}39$

$($constraint $2)$

$2x_1+3x_{2}23$

$($constraint $3)$

$4x_1+8x_{2}38$

$($constraint $4)$

$x_1,x_{2}0$

$($non$-$negativity constraints$)$

What is the slack or surplus associated with the constraint $4$ in the coordinate $(3,1)?$

$8$

$10$

$12$

$18$

None of the above