Answer:
9x^2y^6 square feet.
Explanation:
The area of a square is the length of one of its sides multiplied by itself.
If the side length of a square is -3xy^3 feet,
then the area of the square is
-3xy^3 * -3xy^3 = 9x^2y^6
Therefore, the area of the square is 9x^2y^6 square feet.