Find the missing number?

Answer: Option A

In each star, the value at the centre equals the difference between the sum of the top 3 numbers and the sum of the bottom 3 numbers.

(5 +6 + 4) - (2 + 1 + 3) = 9.
(11 + 4 + 8) - (7 + 3 + 2) = 11.
(9 + 9 + 2) - (6 + 4 + 5) = x
x = 20 - 15
x = 5.