Use the text below to answer the next four questions:

A taco truck manager wants to get more lunch time customers, but doesn't know how much time it takes to process a single customer. The amount of time it takes to process a single customer will help the manager determine the maximum number of customers they can process in the lunch hour. On average, during lunch hour, $12$ customers are in line $($i$.$e$.$ process$)$ waiting to order at the window. Four customers per minute receive their food and leave the line $($i$.$e$.$ exit the process$).$

Flag question: Question $1$

Question $11$ pts

On average, what is the inventory, I $($number of flow units, customers$),$ of the line$/$process during the lunch hour?

Group of answer choices

$4$

$3$