To help you, i'll make the assumption that the side lengths of the small squares are 5 inches long. Well, the area of a square is the side length squared, so if we have 501 of these squares, we can simply multiply the area of one of the small squares by 501.
That is to say if the side length (s) is 5, the area of the square is s2.
If s = 5 ft,
Area of small square = (5ft)2
Area of small square = 25 ft2
Area of the big square = 501 * Area of the small squares
Area of the big square = 501*25 ft2
Area of the big square = 12,525 ft2