Two types of student come to the career-services office for counseling. New students arrive at a rate of 11 students per hour and spend 5 minutes in registration and 10 minutes with an advisor. Returning students students arrive at a rate of 15 students per hour and spend 4 minutes in registration and 7 minutes with an advisor. The staff consists of 2 registration employees and 2 advisors.

How many returning students will be served each hour?