At a Mexican fast-food chain, a customer (a) decides what type of food they want (e.g., burrito, salad, or tacos), (b) decides what fillings they want (e.g., chicken, fish, or vegetable), (c) decides what toppings they want (e.g., lettuce, guacamole, or cheese), and (d) pays for the order that may or may not include a drink.

One employee works at each of the steps (a) through (c), and two employees take care of the payment. Per customer, step (a) takes 2 minutes on average, step (b) takes 3 minutes on average, step (c) takes 1 minute on average, and step (d) takes 4 minutes on average. Suppose another person is hired for step (d), what is the system capacity?