The area of any rectangle is (length) x (width).
Your square is a rectangle, with length=width.
Using 1 inch = 2.54 centimeters, the square's area is
(8 x 2.54 cm) x (8 x 2.54 cm)
= (20.32 cm) x (20.32 cm) = 412.90⁺ cm²
Rounded to the nearest cm², it's 413 cm² .
