[Cobra]

There are 47 cards remaining after the flop. Your opponent could have any one of (47c2) cards or 1081 combinations.

There are two nines and 45 other cards. Either nine could hit with any of the 45 other cards, that makes 90 combinations with one nine. So the probability that you both get top pair is: 90/1081 = 8.3% or 1 in 12 times.

There is also one combination of a pair of nines that we did not include in the above calculation.

Cobra