Let the present age of father be ‘a’ and present age of son be b.

Given, father is three times as old as his son. After twelve years, his age will be twice as that of his son then.

⇒ a = 3b ---- (1)

Also, after twelve years, his age will be twice as that of his son then.

⇒ a + 12 = 2(b + 12)

⇒ a = 2b + 12

⇒ 3b = 2b + 12

⇒ b = 12

Thus, a = 36