To determine how much space Robert will have left for his presentation after using 10 squares with 7-inch sides, we need to calculate the area of the squares and then subtract that from the total area of the poster board.
- Calculate the area of one square:
\[ s^2 = 7^2 = 49 \text{ square inches} \]
- Calculate the area of 10 squares:
\[ 10s^2 = 10 \times 49 = 490 \text{ square inches} \]
- Subtract the area of the 10 squares from the total area of the poster board:
\[ 720 - 490 = 230 \text{ square inches} \]
Therefore, the space Robert will have left for his presentation is 230 square inches.
The correct response is:
230 square inches.