$120\mathrm{.}5$ points

The optimal solution of this linear programming problem is at the intersection of constraints $2$ and $3$

Max $3x_1+4x_2$

$s.t.4x_1+1x_{2}400$

$,4x_1+3x_{2}600$

$,1x_1+2x_{2}300$

$,x_1,x_{2}0$