The first puzzle most people hit in this island is the see-saw. It's a puzzle they gave you a ton of clues about on the hub world. You're trying to balance the see saw so the roller coaster ball can get through this area. Go around and look at the counterbalance they're using. Look at it from BOTH sides. It's 7 wood and 1 crystal pieces.

Did you take notes in the balance games? This means the ball is in essence 11 wood. You want to slide the center point so it's far away from that ball, so you have to make something weighing "22 wood" to balance against it.

How do you make 22 wood? You do it with 1 metal and 2 wood. Yes, 3 pieces. Sneaky, eh? Once you do that, you'll get the code for this section to enter into the first hex spot.

The Myst 3: Exile Walkthrough