Please explain in detail so I can understand how to do it:

Question

A football player punts a ball. The path of the ball can be modeled by the equation y = -0.004x^2 + x +2.5, where x is the horizontal distance, in feet, the ball travels and y is the height in feet, of the ball. How far from the football player will the ball land? Round to the nearest tenth of a foot.

Answer 1

Here is a graph showing the path of the ball

http://www.wolframalpha.com/input/?i=0%3D+-0.004x%5E2+%2B+x+%2B2.5

So the x-intercept would be the distance covered

so -0.004x^2 + x +2.5 = 0
use the quadratice equation were
a = -.004, b = 1, and c = 2.5
x = (-1 ± √1.04)/-.008
= appr. 252.8 or a negative