14.
The first, third and fifth number are even numbers. 2, 8, 12
And the second, forth and sixth numbers are odd numbers. 7, 3, 9
1. y = c + 2x
c1= 2 (and subsequent c= next number in the series) and x is in reducing order:
2 + 2x3 = 8
8 + 2x2 = 12
12 + 2x1 = 14
2. u = a (+-) 2(v).
a1=7 (and subsequent a= next number in the series) and v is in increasing order.
7 - 2x2 = 3
3 + 2x3 = 9
9 - 2x4 = 1
the subsequent number is an even number, so it should be 14