This is how far I got on the very first one.  I could not add a line in the proper spot to extrude, and everytime I tried to extrude it didnt work.  Pretty frustrated with this one.

For the fourth problem, I figured out the circle geometry.  If you look at all the yellow lines, it all lines up.  My trouble was trying to get those lines extruded.  I could not figure out how to get those lines extruded.

This is the third problem on the homework set.  I thought it was pretty easy, but could not round the edges on the blocks in the front.  Other then that this one went smooth.