What should come in the place of question mark in the following series?
$$\text{3, 8, 6, 14, ?, 20}$$

The given series consists of two alternating sub-series:
1. First sub-series (odd positions): $3,6,?$
* Here, the pattern is $+3$:

$$3+3=6$$

$$6+3=9$$

2. Second sub-series (even positions): $8,14,20$
* Here, the pattern is $+6$:

$$8+6=14$$

$$14+6=20$$

Therefore, the missing term is $9$.