Grimrock

So I've been to 3 of the 4 notes in level 4 but I can't seem to find a way past the pits that are on a timer, the ones where you step on the pressure plate and the floor closes up for you to walk on and opens behind you if you aren't fast enough, I've been to the right to get the treasure but I cant seem to find anything else to open the door. http://i.imgur.com/cnbam.jpg

Also how do I get the treasure near the start of level 3? I've been able to open both the doors but don't know how to get the floor to close to walk on it http://i.imgur.com/IwnPf.jpg

When you are approaching the door, look to your left.

Just throw your problems away!