The arch of a stone bridge has the form of a semi-ellipse. The straight horizontal span is 40 meters and the maximum height between the arch and the span is 10 meters. Find the height, in meters, of the arch 10 meters from one end of the span.

- 5
- 5√3
- 2.5
- 7
- 8 2/3

The equation of the ellipse is: