In a school, students thought of planting trees in and around the school to reduce air pollution. It was decided that the number of trees, that each section of class will plant, will be the same as the class in which they are studying, e.g., a section of each class 1 will plant 1 tree, a section of class 2 will plant 2 trees and so on till class 12. There are3 sections of each class. How many trees will be planted by the students?