The bridge, in the shape of a semi elliptical arch, has a span of 120 feet and a maximum height of 25 feet. Choose a suitable rect coord system and find the height of the arch at distances of 10, 30, and 50 feet from center.

I believe this would be the equation for the full ellipse:

x^2/60^2 + y^2/25^2 = 1

but don't know what to do beyond that...

How would I go about finding the height at specific distances from center?