Select the alphanumeric-cluster that can replace the question mark (?) in the following series.
B9U, E16R, H250, ?

Given: B9U, E16R, H25O, ?

Logic: +3 in 1st letters, squares of numbers, -3 in last letters

First Letter Pattern
B + 3 → E
E + 3 → H
H + 3 → K 

Number Pattern
3²=9 → 9

4²=16 → 16

5²=25 → 25
6²=36 → 36

Last Letter Pattern
U - 3 → R
R - 3 → O
O - 3 → L 
Thus, the missing alphanumeric cluster is K36L
Therefore the correct option is (b) K36L