I think I used to live in a twenty-one B.
I might have lived somewhere around 21-B  or 22-B about 20 years ago, but my mind doesn't recall quite if that's correct.
mnli hypothesis: I might have lived somewhere around 21-B  or 22-B about 20 years ago, but my mind doesn't recall quite if that's correct. premise: I think I used to live in a twenty-one B.