let's question a question

Number of the student who have opted for the subject A, B, and C are 84, x, and 108 respectively. The examination is to be conducted for these students such that only the students of the same subject are allowed in one room. Also the number of students in each room must be same. What is the minimum number of rooms that should be arranged to meet all these conditions?
(1) 28
(2) 60
(3) 12
(4) 21

If (4) is the correct choice as answer, what is x?

(A) 12
(B) 14
(C) 21
(D) 28
(E) 60