HURRY HELP!!!

A grade-school instructor teaches math, English, and history. This year, the teacher has 100 homework papers to correct every week (one per student per class). Suppose that the math and English classes have the same number of students in them, and that the questions on each homework assignment number 10, 20, and 30, respectively. If the teacher corrects 2,100 homework questions every week, how many students are In each class?
(Hint: Use Gauss-Jordan elimination.)