I found other versions of this question but when I followed all the steps I keep getting the wrong answer...
A cooling tower for a nuclear reactor is to be constructed in the shape of a hyperboloid of one sheet. The diameter at the base is 280 m and the minimum diameter, 500 m above the base, is 180 m. Find an equation for the tower. (Assume the center is at the origin with axis the z-axis and the minimum diameter is at the center.)

The answer I got (that is wrong) is (x^2)/8100+(y^2)/8100-(z^2)/(419.627^2) = 1

Question

I found other versions of this question but when I followed all the steps I keep getting the wrong answer...
A cooling tower for a nuclear reactor is to be constructed in the shape of a hyperboloid of one sheet. The diameter at the base is 280 m and the minimum diameter, 500 m above the base, is 180 m. Find an equation for the tower. (Assume the center is at the origin with axis the z-axis and the minimum diameter is at the center.)

The answer I got (that is wrong) is (x^2)/8100+(y^2)/8100-(z^2)/(419.627^2) = 1