I don't quite understand the question or something seems to be missing. From what I can see, there are many numbers that meet the criteria.
Let N be the denominator and N the numerator.
We are told that D = 2N + 2
If we try a random series of numerators, we get valid answers for the resulting denominator:
The list is infinite. It would seems any of them meet the needs of the question. I don't see a way to pick iust one.