The path of a golf ball can be modeled by the quadratic equation y=-0.001x^2+0.3x, where y represents the vertical distance and x represents the horizontal distance that the ball has traveled in yards. how far does the ball travel before it hits the ground?

Well if y represents the vertical distance of the ball then you want to solve the equation for when y is 0, since 0 would represent the ball being on the ground.  So substitute 0 in for y and solve the equation.

0 = - 0.001x^2 + 0.3x

we have a common factor of x in both terms so we can take that out.

0 = x(-0.001x + 0.3)

Zero product property tells us that we can set both of those products equal to zero and solve

0 = x
0 = -0.001x + 0.3

our first answer is x = 0 is obvious bc thats when the ball starts before you hit it, means it traveled 0.

solving the second equation gives us x = 300 

so the ball traveled 300 "yards" I suppose your problem starts, which is impossible, but no matter thats the answer :-)