LeBow Cafeteria has four windows: salad, sandwich, dessert, and drink. Each customer spends on average 5 min, 3min, 1min and 1min at each window. There are 2, 4, 1, and 1 people serving at each window, respectively. Arriving customers first visit the salad bar and sandwich window, and among them only 80% visit dessert window, while the other 20% leave the cafeteria after buying sandwich. Only 50% of all customers visit drink window, while the others leave after buying dessert.