Okay, I'm trying to draw them out and rotating them in my head.. see if their mirror images match.
For number 2, I get 4 stereoisomers rather than 3 (which is the answer). I drew a mirror image of the molecule and tried to see if is superimposable, but I got another configuration of that molecule that has a non-superimposable mirror image as well, doesn't that make it 4 possible stereoisomers?
Edit: How do I check for planes of symmetry for 3D molecules such as the one posted above? It's quite confusing...