Complete the series: 3, 8, 6, 14, ______, 20?

Complete the series: 3, 8, 6, 14, ______, 20?

Explanation

In the question above,

3 × 2 + 2 = 8

6 × 2 + 2 = 14

Similarly, if we take '?' as 'a'

a × 2 + 2 = 20

a × 2 = 18

a = 18/2

a = 9