Consider a sequential process with $3$ stations. The processing time $($minutes per unit by $1$ employee$)$ and number of employees at each station are as follows:

$\backslash$table$[[,$Processing time,Number of Employees$],[$Station A: $6mi\frac{n}{?}$ unit,$3$ employees,$],[$Station B: $2mi\frac{n}{?}$ unit,$4$ employees,$],[$Station C: $6mi\frac{n}{?}$ unit,$6$ employees,$]]$

What is the process capacity $($for the whole process$)?$

$6$ units per hour

$30$ units per hour

$20$ units per hour

$6$ units per minute