When brain teasers involve numbers, it can get tricky.  For some reason, your brain begins to second guess itself.  This brain teaser isn't as hard as you'd think.

Take a look at the circle of numbers.  There has to be a pattern, right?  Yes, there is a pattern.  Take any number and the number directly across from it.  Then add them together.  It doesn't matter which sections you choose, the two across from each other equal 44.

Therefore, the answer is 9.  Simple, right?