Suppose a retail store utilizes a multiple$-$server waiting line model with three servers $($k $=3)$ and with arrival times following a Poisson distribution and service times following an Exponential probability distribution. Assume the arrival rate lambda $=18$ customers per hour and the service rate mu $=20$ customers per hour for each server. Using this information what is the average number of customers in the waiting line?Report your solution out to two decimal places.