Let the ages of Ani, Biju, Dharam and Cathy be a, b, c and d respectively.

Given, ages of two friends Ani and Biju differ by 3 years. Ani’s father Dharam is twice as old as Ani and Biju as twice as old as his sister Cathy. The ages of Cathy and Dharam differ by 30 years.

a – b = 3

c = 2a and b = 2d

c – d = 30

Solving the above four equations

⇒ 2a – b/2 = 30

⇒ 2a – a/2 + 3/2 = 30

⇒ a = 19

Thus, b = 16 years