Weary travelers arrive at SeaTac International$$ Airport, pick up their$$ luggage, stumble to their$$ cars, and proceed to the parking lot attendant to pay for their parking. Traveler$$ inter$-$arrival times are exponentially$$ distributed, as are the service times of the attendant. On$$ average, travelers arrive every $25$ seconds. The attendant can process three travelers per$$ minute, and processing rates follow a Poisson distribution.

Use the information in the scenario above. How many minutes per hour is the attendant not serving$$ customers?