Owners of a local restaurant are concerned about their ability to provide quality service as they continue to grow and attract more customers. They have collected data from Friday and Saturday nights, their busiest times of the week. During these time periods about 75 customers arrive per hour for service. Given the number of tables and chairs, and the typical time it takes to serve a customer, the owners estimate they can serve on average about 100 customers per hour. During these nights, are they in the zone of service, the critical zone, or the zone of nonservice?