Three hairstylists, Francois, Bernard, and Mimi, run Fast Service Hair Salon for busy professionals in the Gold Coast area of downtown Chicago $($see Figure $5\mathrm{.}1).$ They stay open from $6$:$45$ am to $9$:$00$ pm in order to accommodate as many people$$s work schedules as possible. They perform only shampooing and hairstyling activities. On average, it takes $10$ minutes to shampoo, $15$ minutes to style the hair, and $5$ minutes to bill the customer. When a customer arrives, he or she first checks in with the receptionist$($Bernard$$s younger sister LuLu$).$ This takes only $3$ minutes. One of the three stylists then takes charge of the customer and performs all three activities$$ shampooing, styling, and billing$$ consecutively.