Consider a production line has six serial stations $($A$-$B$-$C$-$D$-$E$-$F$).$ The following table shows the process times in minutes $($or minutes$/$unit$)$ of the six stations.

$\backslash$table$[[$Station$,$Process Time $($minutes$/$unit$)],[$A$,9],[$B$,10],[$C$,7],[$D$,12],[$E$,15],[$F$,4]]$

What is the capacity of the entire system?

$\frac{1}{15}$ unit$/$minute

$57$ minutes

$\frac{1}{12}$ unit$/$minute

$15$ minutes