A manager of a taco stand is interested in advertising 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 amount of customers they can process in the lunch hour. On average, during lunch hour, there are 12 people in line waiting to order at the window. 4 people per minute leave the taco stand after receiving their food. On average how long do customers wait in line?