Consider the following LP model:

Maximize $15x+20Y$

subject $to$: $1x+5Y250hrs(carpentry$ time$)$

$,4x+7Y440hrs(painting$ time$)$

$,2x+4Y300hrs(assembly$ time$)$

$,x,Y0$

Determine the slack time in assembly for the solution, $x=30$ and $Y=40.$

$40$

$80$

$10$

$20$