Start by reviewing the basic equations for an ellipse:
https://en.wikipedia.org/wiki/Ellipse
The simplest standard form:
x2 / a2 + y2 / b2 = 1
For a "horizontal" ellipse, a is larger than b and a is called the "semi-major axis", and b is the "semi-minor axis".
c is the distance from the center to each focus, and c = √(a2 - b2 )
You are given the total width, and the distance between the foci. This allows you to calculate the semi-minor axis, which is the distance from the horizontal axis to the top.
BUT--there is an ambiguity in the problem statement: If the "rings" are at the foci, then the ellipse equation gives us the vertical distance from the rings to the top of the ellipse. To get the total height of the building, we need the height of the rings above the floor.