36-9=25 thus it isn't possible because it's not between 31 and 37. 48-9=39 hence also not possible. However for 42, it is defintely possible. Thus answer is 7
Totally going on a limb and answering this right now for the fun, but really hoping to help. So multiples of 6. If you start at 6(6)=36. 9 less than 36 isn’t between 31 & 37. However, when you go to 6(7)=42, 9 less than 42 is 33 and 33 does indeed lie between 31 & 37. My final answer would be 33.
