Solution; 

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

Given:

Sum of father's and his son's age is 60. So,

$x + y = 60 ------> 1$

Before six years,

father's age will be (x - 6) and son's age will be (y - 6)

It is given that,  $(x - 6) = 5(y - 6)$

$x - 6 = 5y - 30$

$x - 5y = -30 + 6$

$x - 5y = -24$

Substituting 1 in here we get

$60 - y - 5y = -24$

$60 - 6y = -24$

$- 6y = -24 - 60$

$- 6y = - 84$

$6y = 84$

$y = 84/6$

$y = 14$

The present age of son is 14 years . After 6 years his age will be ,

$14 + 6 = 20$ years.

The correct option is 3). 20