Find the Total Volume of a Pool:

As viewed from above, a swimming pool has the shape of the ellipse

x^2/900+y^2/400 = 1

The cross sections perpendicular to the ground and parallel to the y-axis are squares. Find the total volume of the pool. (Assume the units of length and area are feet and square feet respectively. Do not put units in your answer.)

V =

how do I do this problem?

I've tried several different formulations, and I figured the answer was Int (subscript -30, superscript 30) (X^2)-900 dx but this does not appear to be the correct answer.