(b) Let the present age of father be 3xand daughter be x
So, 4 yr ago, father's age and daughter's age was (3x - 4) and (x - 4) respectively.
Therefore,
=3x - 4 = 4x - 16 ⇒ x = 12 yr
∴ Daughter’s present age, x = 12 yr
and father's present age, 3x = 3 x 12 = 36 yr
∴ Present average age =
= 24 yr
2 yr hence average age = 24 + 2 = 26