Correct Answer - Option 3 : 24
The pattern followed here is:
Reverse the number then add consecutive integers.
starting from 21
12 + 1 = 13 , reverse it,
31 + 2 = 33,
33 + 3 = 36,
63 + 4 = 67,
76 + 5 = 81,
18 + 6 = 24,
42 + 7 = 49,
94 + 8 =102,
Hence, 24 will be the correct answer.