In lab 44.5, before you can mount /dev/cdrom to /mnt/source, you'll need to mkdir 'source' under mnt - that said, that should be obvious to anyone who gets to the last lab!
LS216, here I come...
Well, that's a minor thing, as it's an administration course. We expect the students on this level to be able to solve this kind of things.
I see you are seriously advancing on the course, best wishes!