I found that the most difficult part of this game (with Carnby/the guy) was the combination dials in the library. I couldn't figure out the code to save my life, but I did.
During the game you with find two pieces of a torn photograph. There are numbers on the back of each torn piece.
When you get both sides of the photograph, put the photograph together and add both numbers together to get the right number for the library combination lock and the door behind the bookshelf will open.