please answer questions 7a-7b

7) 7 points. A parabolic arch is used in the foilowing bridge. The bridge is 500 feet long. If the origin is used as the vertex with the positive x axis going to the right following the bridge then a point on the arch is (80, -40). m l a) Determine an equation for this parabola. bi Determine the length of the vertical support 250 feet to the right of the origin (the value indicated with '3')