At BCD car wash, when a customer arrives, he or she first checks in with a receptionist and then leaves the car to one of several car washers. While the customer is waiting for the car to be washed, he or she proceeds to pay at the cash register. After the payment, the customer returns to his/her car when it is done and then leaves. On average, reception takes 3 minutes. Car wash takes 5 minutes. Paying at the cash register takes 4 minutes. Returning to car and leaving requires 2 minutes. Currently, the car wash employs 1 receptionist, 2 cash registers and 3 car washers. What is the theoretical flow time (in minutes) of the process?