Ok. There is two answers, the obvious one being 40:
1 + 4 = 5
2 + 5 = 12
3 + 6 = 21
8 + 11 = 40
Now, the catch is, the problem suggests you need to feel the void between 3+6 though 8+11.
1 + 4 = 5
2 + 5 = 12
3 + 6 = 21
4 + 7 = 32
5 + 8 = 45
6 + 9 = 60
7 + 10 = 77
8 + 11 = 96
So, the real problem is, there is actually two right answers or just one?
Personally, i think 96 is the only right answer.