Correct answer is: 7 years

Solution :

Let us take the present age of father and his son as 'x' and 'y' .

Given:

The father's age before 4 years is 8 times the age of his son

x - 4 = 8( y - 4)------> 1

At present, father's age is 4 times the age of his son

x = 4y ------> 2

Substituting equation 2 in 1 we get

4y - 4 = 8y - 32

8y - 4y = 32 - 4 

4y = 28

y = 28/4

y = 7

Substituting the value of y in equation 2 we get

x = 4 × 7

x = 28

The present age of son is 7 years.

The correct option is 2). 7 years