Correct option is B
Let the age of A and B after ten years be 13x and 10x respectively.
ATQ,
(13x-10)-(10x-10)=6
3x=6
x=2
Required age = 10x-10=20-10=10 years
Alternate solution,
The difference between age of any person is always same.
So,
13x – 10x = 6
3x = 6
2 = x
Age of B = 10x – 10 = 10 years