Sarah is lining a square tray with 1 inch square tiles. the side length of the tray is 9 inches. How many tiles does Sarah need?

To find the total number of tiles that Sarah needs, we need to calculate the area of the square tray and then divide it by the area of each individual tile.

1. First, we find the area of the square tray. Since the side length of the tray is given as 9 inches, the area can be calculated by squaring the side length.
\text{Area of tray} = (\text{side length})^2 = 9^2 = 81 square inches.

2. Next, we find the area of each individual tile. Each tile is a square with a side length of 1 inch, so the area can be calculated by squaring the side length.
\text{Area of each tile} = (\text{side length})^2 = 1^2 = 1 square inch.

3. Finally, we divide the area of the tray by the area of each tile to find the total number of tiles needed.
\text{Total number of tiles needed} = \frac{\text{Area of tray}}{\text{Area of each tile}} = \frac{81 \, \text{square inches}}{1 \, \text{square inch}} = 81 tiles.

Therefore, Sarah needs 81 tiles in total.

ANSWER: 81 tiles