A small company just just opened a new massage station at Philadelphia airport. The company has a stand that offers massages to travelers. Customers can select a length of massages between 5 and 20 minutes and there is a unique rate of $30 independently of the length selected by customers. The average length of massage requested by customers is of 15 minutes with standard deviation of 10 minutes.

There are 6 employees delivering massages. The average number of potential customers requesting a massage is of 20 per hour. The inter-arrival times are assumed to be exponentially distributed . If no spot is available when the customer arrives, s/he leaves in order not to risk missing his/her flight.

What is the average number of customers serviced per hour? (You should be accurate up to two decimal places after the decimal point.)