What will come in place of the question mark (?) in the following series?
$$\text{LA},\text{MC},\text{OF},\text{RJ},?,\text{AU}$$

Let's split each cluster into its first and second letters to evaluate the two independent underlying patterns:
First Letter Series: L, M, O, R, ?, A

* $L\stackrel{+1}{\to }M$
* $M\stackrel{+2}{\to }O$
* $O\stackrel{+3}{\to }R$
* Following this increasing gap pattern, the next step should be $+4$:
$R\stackrel{+4}{\to }V$
* Check verification for the final step ($+5$):
$V\stackrel{+5}{\to }A$ (since $22+5=27\equiv 1=A$). This is correct.

Second Letter Series: A, C, F, J, ?, U

* $A\stackrel{+2}{\to }C$
* $C\stackrel{+3}{\to }F$
* $F\stackrel{+4}{\to }J$
* Following this increasing gap pattern, the next step should be $+5$:
$J\stackrel{+5}{\to }O$
* Check verification for the final step ($+6$):
$O\stackrel{+6}{\to }U$ (since $15+6=21=U$). This is correct.

Combining the two letters gives VO.