Consider the following formulation:

Max $2x+4y$

$S.T.$:

$6x+2y20$

$x1$

$x+y4$

$x,y0$

If the optimal solution is $x=1$ and $y=2,$ what is true about the $3$ rd constraint $x+y4?$

The constraint is binding

The slack is $1$

The surplus is $1$

None of the above