A suburban specialty restaurant has developed a single
drive-thru window. Customers order, pay, and pick up their food at
the same window. Arrivals follow a Poisson distribution while
service times follow an exponential distribution. If the average
number of arrivals is 8 per hour and the service rate is 5 every 15
minutes, what is the average number of customers in the waiting in
line behind the person being served. Leave your answer with 2
decimals when necessary and use (.) as decimal separator instead of
(,).