During the busy lunch period at the Atrium Caf$,$ customers arrive at the rate of $200$ customers$/$hour$.$ Studies have indicated that $30\%$ of the customers order their lunch from the Grill, and $50\%$ of customers get lunch from the Deli $($the remaining $20\%$ just get self$-$service items$).$ All customers pay for their food at the cash register. On average, the grill$-$chef takes $40$ seconds to serve a customer, the deli$-$chef takes $30$ seconds, and the register$-$clerk takes $12$ seconds. $($Assume that all service time and interarrival times are distributed exponentially, and that there is one employee at each of the three stations.$)$