Find the missing number?

Answer: Option C

Logic:
First number + second number - 4 = Third Number.

3 +6 - 4 = 5
6 + 5 - 4 = 7
5 + 7 - 4 = 8
8 + 7 - 4 = 11
11 + 8 - 4 = 15
15 + 11 - 4 = 22.
So,
Missing number = 22.