The age of father is four times as much as the sum of the age of his three children but 6 years hence his age will be only double the sum of their ages. Find the age of the father.

60 years

let age of father = x and age os sum of his 3 children = y 

ATQ, 

x = 4y 

 after 6 years 

( x + 6 ) = 2 ( y + 6 +6 + 6 )    [6 is added thrice for three children ]                       

x  = 2y + 30

put x = 4y 

 4y = 2y + 30

 2y = 30

 y = 15 

 so age of father is x = 4 × 15 = 60 years