There are four classes in Grade 6, 84 students in class 1 and class 2, 136 students in class 2 and class 3. Class 2 accounts for 25% of the whole grade, best Don't use equations

There are four classes in Grade 6, 84 students in class 1 and class 2, 136 students in class 2 and class 3. Class 2 accounts for 25% of the whole grade, best Don't use equations

If there are three classes in all, they are similar
(84+136)/(1+25%)=176
Four classes can't find out