The optimal solution of this linear programming problem is at the intersection of constraints

$1$

$$and

$2$

$.$

Max

$2$

x

$1$

$+$

$$x

$2$

s

$.$

t

$.$

$4$

x

$1$

$+$

$1$

x

$2$

$<$

$=$

$4$

$0$

$0$

$4$

x

$1$

$+$

$3$

x

$2$

$<$

$=$

$6$

$0$

$0$

$1$

x

$1$

$+$

$2$

x

$2$

$<$

$=$

$3$

$0$

$0$

x

$1$

$,$

$$x

$2$

$>$

$=$

$0$

$$ Over what range can the coefficient of

x$1$ vary before the current solution is no longer optimal?