A small company just opened a new ma{sage station at Philadelphia airport. The company has a stand that offers massages to travelers. Customers can select a length of massage 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 five employees delivering massages. The average number of potential customers requesting a massage is of 40 per hour. The inter-arrival times are assumed to be exponentially distributed.

If no spot is available when the customer arrives, she leaves in order not to risk missing her/his flight.

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