First, illustrate the problem:
24 feet is the distance between the tree and the mirror.
4 feet is the distance from Irene's eyes to the mirror.
5.5 feet is the distance of Irene's eyes from the ground.
4 feet is the distance of Irene from the mirror
From this, we can draw a right triangle and then use the Pythagorean theorem to solve for the height of the oak tree. Also, we have an option to use ratio and proportion between two similar triangles.
Well...The sum of those radicals is 7 root 2 and that is a imperfect square root so this is irrational
4y:5y would be the simplest form
I assume the base of S is the disk centered at the origin, or x² + y² ≤ r². Solving for y gives two solutions corresponding to the upper and lower halves of the circular boundary,

and the vertical distance between them - i.e. the side length of each cross section - is

Then the volume of each square cross section 4 (r² - x²) ∆x, and the volume of S is

By symmetry, this is the same as

which gives a volume of
