4, 8, 12, 7, 11, 18, 9, ------------------------, 22
12
15
13
7
11
4, 8, 12, 7, 11, 18, 9, ------------------------, 22
In this series, third number is the sum of first two numbers like 4+8=12, 7+11= 18
So, at the end, 9+x= 22
x= 13