Gabi is helping her friend Joaquin create a square tile design in his backyard. Joaquin has one large square tile that is no longer being manufactured. He also has eight rectangular tiles that have the same side length as the large tile, and one small square tile that has the same width as the rectangular tiles. Gabi gets her algebra tiles to model the situation. How many small square tiles does Joaquin need to buy to complete a square tile design? ​