Which of the following letter-number cluster will replace the question mark (?) in the given series? UDF6, VFI9, ?, XJO15, YLR18, ZNU21

Explanation

The pattern in the series involves incrementing letters and numbers: - U → V → W → X → Y → Z (1st letter increments by 1). - D → F → H → J → L → N (2nd letter increments by 2). - F → I → L → O → R → U (3rd letter increments by 3). - Numbers: 6 → 9 → 12 → 15 → 18 → 21 (increment by 3). Thus, the missing cluster is WHL12.