Hi abby, I merged this post with your other Ghost of Thornton Hall topic that you had already started so that all your questions about the game will be in the same thread.
Take a look at MaG's walkthrough for this portion of the game and you will see that each line of each square corresponds to a number. If you click on each line in turn with the correspondingly correct numbers, the briefcase will open.
Let me know if this doesn't help.