Calling all math's genius to try this.... and prove the logic...
 
The mum is 21 years older than the child.
In 6 years from now the mum will be 5 times as old as the child.
 
Question:
Where's the father?
Try first, before you check the answer below!

Solution:
The mum is 21 years older than the child.
M = C + 21
In 6 years from now the mum will be 5 times as old as the child.
M + 6 = (C + 6) x 5
Hence,
C + 21 + 6 = (C + 6) x 5
C + 27 = 5C + 30
-3 = 4C
C = -3/4
The child is -3/4 years old, it'll be born in 9 months.

So right now, the father is on top of the mother