HELPPPPP!!! Hyperpola and Ellipse word problem

(1) A hyperbolic reflector for a radiotelescope has the equation :

y^2/900-x^2/225=1.

If the reflector has a diameter of 20 feet, how deep is it (in feet)?

(2)A nuclear cooling tower is in the shape of a hyperboloid(that is, a hyperbola rotated around its conjugate axis). The equation of the hyperbola is :

x^2/5625-y^2/10000=1

If the center of the tower (the narrowest part) is 100 feet above the ground, what is the diameter (in feet) of the circular base?

(3) A semi-elliptical arch in a bridge over a river has a span of 40 feet and a clearance of 12 feet above the water in the middle of the bridge. How much distance (in feet) above the water is there 5 feet from the banks?

PLLLLEEEASSSE help set these up for me.