It’s back to the classroom for students at Maine’s state universities. Classes begin Tuesday at the flagship campus in Orono, the University of Southern Maine, and university campuses in Fort Kent, Presque Isle and Augusta. Classes begin Wednesday at campuses in Farmington and Machias. More than 30,000 students attend classes at the seven schools each fall. The University of Maine at Orono has the largest enrollment with more than 11,000 students, followed by the University of Southern Maine, which had more than 9,300 students on its campuses in Gorham and Portland last fall.