In a large urban high school, all students are assigned to a homeroom. one of those homerooms has 30 students in it, and all the others have 27 students. in each homeroom with 27n students, three students were chosen at random to participate in a survey. in one of the homerooms with 30 students, 4 students were chosen. if the school has exactly 3000 students, how many of them took part in the survey?