Correct Answer - Option 3 : 88

**Given:**

The original ratio of student in three classes is 3 : 13 : 6

**Calculation:**

Let be assume the at the beginning students in three-class were 3x, 13x, and 6x respectively and after ratio was 15y, 35y, and 21y respectively.

⇒ 3x - 15y = -18 ..... (1)

⇒ 13x - 35y = - 18 .... (2)

By solving (1) and (2)

⇒ x/y = 2/1

⇒ From equation (1)

⇒ x = 4, y = 2

⇒ The total number of student in all classes = 3x + 13x + 6x = 22x = 22 × 4 = 88

**∴ The required result will be 88.**