This is a permutation problem so we just have to add up what is possible.
You have two scenarios - either the first number is part of the pair or it isn't.
When the first number is part of the pair you have 3 available for the first digit (7,8&9), then only one number will match those and there are 9 numbers available for the third digit. so 3(1)(9)=27. you have to multiply this by two becuase switching the 2nd and third digits will give you different numbers so we are up to 54.
The second scenario is when the first digit is not part of the pair that are equal to each other. We still have three digits available for the hundreds digit then 9 for the second digit and only 1 will match - for (3)(9)(1)=27 We dont' multiply these by 2 becuase that would create the same number (711/711). for a total of 81.
But, in the second scenario we included 700 and the question clearly says the integers greater than 700 so we have to 1 from the total to get 80. Answer is C[spoiler][/spoiler]
Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA
