It varies by course right? I had about 18h a week, as did my bio friends. Electrical engineers got about 25-30. Our resident medical student seemed to have about 90. The rare occasion he was around he had books out, and he as first year at the time!

Then there were the ones in history and arts who got 6-12 a week. I'm not saying they didn't get a ton of work to do outside classes (I have no idea how much they did) but if you have 6 lectures a week you may be expected to attend 100% vs if you have 30.