The answer is

12.

Solution

The trick here is about rearranging the order and analysing. Take the first row and rearrange it in the increasing order and at the same time, below to it, rearrange the second row in decreasing order:  2 3 4 5 6 (7) 8 16 14 12 10 8 (6) 4

The answer is

12.

Solution

The trick here is about rearranging the order and analysing. Take the first row and rearrange it in the increasing order and at the same time, below to it, rearrange the second row in decreasing order:
first row-----second row:
2-----16
3-----14
4-----12
5-----10
6-----8
(7)-----(6)
8-----4

So for 4 its 12.