You plan to install a single-occupant restroom for a new, small restaurant. It is estimated that on the average, there would be 6 customers needing to use the restroom per hour. It is estimated that on the average, a customer 3 uses the restroom for 4 minutes. Assume that both the inter-arrival time and the time duration a customer uses the restroom can be well described by the exponential distribution.

What is the probability that more than two customers are waiting in line for the restroom?