Thanks for the puzzle.
The series may be explained as below: 9 + 3 = 12 12 - 1 = 11 11 + 3 = 14 14 - 1 = 13 So the next number should be 13 + 3 = 16 and 16 - 1 = 15. So the answer is 16
There are 2 series.one is 11,13,15 and other is 12,14,16 Hence answer is 16.
The number is 16 9, 12, 11, 14, .13, 16,15,
Consider alternative terms:
we get 9,,11,13,15 and 12,14,16 therefore answer is 16
9+3=12 11+3=14 13+3=16 15+3=18