It would be 3. This is because the riddle goes:
I am a number with a couple of friends, a quarter a dozen, and you'll find me again. What am I?
Its says "a quarter a dozen" a quarter a dozen is 3 because 3 multiplied by 4 is 12. 3 is the quarter part of the dozen (12). This is a easy riddle it doesnt get more complicated than that. If not look up the riddle yourself, I am sure tommarvoloriddle found it on a website somewhere.