Which of the following letter-clusters will replace the question mark (?) in the given series to make it logically complete?
FAN15, KFS20, PKX25, UPC30, ?

Given Series:
FAN 15, KFS 20, PKX 25, UPC 30, ?
Letter Pattern: Letter is increasing by 5 places.
First letters: F → K → P → U → ?
F → K → P → U: Moves +5, +5, +5.
U → Z: Next letter in the pattern is Z.
Second letters: A → F → K → P → ?
A → F → K → P: Moves +5, +5, +5.
P → U: Next letter is U.
Third letters: N → S → X → C → ?
N → S → X → C: Moves +5, +5, +5.
C → H: Next letter is H.
Number Pattern: Number is increasing by 5.
15, 20, 25, 30, ?

15+ 5 = 20, 20 + 5 = 25, 25 + 5 = 30, 30 + 5 = 35
So, ZUH 35 is the correct answer.

Thus, correct  option is (d).