The puzzles are labeled in order 1, 2, 3. This tells you that you should consider the answer to the first puzzle (matchsticks), the second puzzle (illustration of the kid's room), and now this one. 

You're looking at playing cards with sticky notes on them. 

Use the answer to the matchstick challenge and the answer to the photo challenge (the kid's room) to know which card to choose.  If the answers you got do not correspond with a card on the green felt, go back and try to get another answer. 

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Then, use the letter on that card. Set it aside until you solve the other pathways.