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

Correct option is A

Let's break down the pattern in the given series:
First Letter Pattern:
U, V, ?, X, Y, Z
Here, the first letters are increasing by 1 position in the alphabet:
U → V → W → X → Y → Z
So, the missing first letter is W.
Second Letter Pattern:
D, F, ?, J, L, N
Here, the second letters are increasing by 2 positions in the alphabet:
D → F → H → J → L → N
So, the missing second letter is H.
Third Letter Pattern:
F, I, ?, O, R, U
Here, the third letters are increasing by 3 positions in the alphabet:
F → I → L → O → R → U
So, the missing third letter is K.
Number Pattern:
6, 9, ?, 15, 18, 21
Here, the numbers are increasing by 3:
6 → 9 → 12 → 15 → 18 → 21
So, the missing number is 12.
Thus, the missing cluster is WHL12.
Therefore, the correct answer is (A) WHL12.