Correct option is D
In this question following logic is followed-
1st × 3 + 3 = 2nd Number
Option (a) 2 : 9 → 2 × 3 + 3 = 6 + 3 = 9
Option (b) 6 : 21 → 6 × 3 + 3 = 18 + 3 = 21
Option (c) 10 : 33 → 10 × 3 + 3 = 30 + 3 = 33
Option (d) 8 : 29 → 8 × 3 + 3 = 24 + 3 = 27 ≠ 29
Therefore, the correct answer is (d).