Consider the following four step process:

$4$ stage process.png

The following data are available for the four steps:

cid:clip$\_$image$004.$png

Suppose the steps in activity D are made easier, so the activity time per unit in step D is reduced by $50\%($to $0\mathrm{.}25$ min per unit$).$ If the assignment of workers to steps remains the same, by how much does the capacity of the entire process increase in units per min?

Question $3$ options:

$4$

no change

$1$

$2$

$6$