Question 1038139
-x^2+2x+8
The vertex is at -b/2a and the x value is -2/-2 or 1. The y-value is -1+2+8=9
The y-intercept is at (0,8)
{{{graph(300,200,-10,10,-10,10,-x^2+2x+8)}}}
The vertex is 9 feet from the floor or the y-axis in this instance.
Other questions ask about the floor space under the arch, and that is 6 feet, judging by the x-intercepts.