What is the probability that there are exactly two customers waiting in the waiting area?

Georgette Scissors is Kristines favorite hair stylist in University City. Georgette is a highly tal- ented hair stylist, and very patient too. She listens carefully what her customers want, and always accommodates her customers' requests on style. Since she is so patient and accommodating to her customers' requests, the cutting times are highly variable and follow an exponential distribu- tion. It take Georgette, on average, 20 minutes to serve one customer. Assume that the customer arrival to Georgette's Salon follows a Poisson distribution, and the av- erage arrival rate is 2 customers per hour. When a customer arrives, if Georgette is busy serving another customer, the arriving customer will wait patiently in the waiting area. All customers are served in the order of their arrival (first-come-first-served)