I just got it as close to there as I could and it worked. I was off by at least 2 or 3 numbers in each direction.
The true destination is the intersection of a line drawn from to 3-2-5 . In practice, this midpoint is located exactly beneath the Solomon Wayne Courthouse , in a flooded sewer junction that is not marked on the standard map. batman arkham city decode broadcast 2-7-5 3-2-5
for your given input: If the game says "2-7-5 3-2-5", try entering "BEFORE" — that’s what Rocksteady intended for that riddle (the last digit is often misremembered as 5 when it’s actually 6). I just got it as close to there as I could and it worked