Answer:
F. 5
Explanation:
For 9 to be a common factor, x must be a multiple of 9. For the greatest common factor to be 9, not 18 or 36, x must be an odd multiple of 9.
There are 5 2-digit odd multiples of 9:
27, 35, 63, 81, 99
There are 5 possible 2-digit values for x.