(81 - 63) , (24 - 48) , (21 - 15) , (13 - 39)
Option:
Justification: This is the only group in which the sum of the digit of both the numbers is the same.

(81 - 63) , (24 - 48) , (21 - 15) , (13 - 39)
Justification: This is the only group in which the sum of the digit of both the numbers is the same.