Find the Volume of the described solid S.

The base of S is an elliptical region with boundry curve 9x^2 + 4y^2 = 36.Cross sections perpendicular to the x-axis are isosceles triangles with hypotenuse in the base.

The answer in my book is 24, I cant seem to even imagine the region I tried drawing the graph of the elliptical region, am not sure how the cross sections will look like? Any help much appreciated thanks