Area of a regular polygon = 1/2 (apothem) (perimeter)
*substitute the givens
20000 sq. feet = 1/2 (80 feet) (Perimeter)
*multiply the equation by 2
40000 sq. feet = 80 feet (Perimeter)
*divide by 80 feet
500 feet = Perimeter
it says that the polygon has 20 sides and the formula for the perimeter of the polygon is by adding all its sides
so,
20(length) = Perimeter
20(length) = 500
length = 25 feet
Therefore, the length of each side of the polygon is 25 feet.