Find the missing number?

Answer: Option B

Sum of the upper left element of all outer diagram - 5 = Lower left Element of the middle circle. I.e
3 + 0 + 5 + 9 - 5 = 12.

Sum of the upper right element of all outer diagram - 5 = Upper left Element of the middle circle. I.e.
1 + 1 + 2 + 5 - 5 = 4.

Sum of the lower left element of all outer diagram - 5 = Lower right Element of the middle circle. I.e
6 + 2 + 6 + 0 - 5 = X
X = 9.
Missing Number = 9.