It depends on what size keg and what sized case. I'll answer for the standard sizes in the US. In the US a keg is 1/2 barrel, or 15.5 gallons. A case is usually 24 12oz bottles. 15.5 gallons is 1984...
Beer generally comes in 6-packs and 12-packs (and here in Canada in 24-packs, but that's apparently just a Canadian thing). By "case" it sounds more like a 12-pack, but it could just as easily be a...