Find the volume V of the described solid S.

A) The base of S is an elliptical region with boundary curve 16x2 + 9y2 = 144. Cross-sections perpendicular to the x-axis are isosceles right triangles with hypotenuse in the base.

B) The base of S is the region enclosed by the parabola y = 7 ? 7x2 and the x-axis. Cross-sections perpendicular to the x-axis are isosceles triangles with height equal to the base.

C) The base of S is a circular disk with radius 2r. Parallel cross-sections perpendicular to the base are squares.