16 seats in Biz on the 757s.
You can also infer demand from the availabilities over time. Z is the lowest business fare, C the highest. A flight showing C9 D0 J0 Z0 probably means they have got strong demand, and really genuinely only have 9 seats left. C9 D4 J0 Z0 means they've sold a few, but are still discounting to fill a few more.
Seeing C9 D9 J9 Z9 a couple of days before a flight goes often means there's not much evidence of demand, and possibly only a couple of seats sold.
You can also look at what inventory has been dumped into R (which is Star Upgrade) and I (which is Star Award). BRS-EWR is usually available in both on weekdays. EWR-BRS usually not, but that seems to be general CO policy not to give away the night flight inventory to anywhere (not just BRS).