About Co-21B: Co-21B is a support class for students currently enrolled in MAT 21B. In each co-class, you will review recent topics presented in your lecture and work through practice problems. Co-class is a great opportunity to get clarification on tricky topics, since it is much smaller than your lecture and you are encouraged to ask questions. To enroll in Co-Class, you can visit the AATC Math website to find the schedule and CRN. If you don't want to enroll for a workload unit, you can still be added to the Canvas page for co-class and attend as often as you wish. Email the co-class instructor to be added to Canvas without enrolling.