You can model an arch at your school using the equation y=−0.9(x+3)(x−3), where x and y are measured in feet. The x-axis represents the ground. Find the width of the arch at ground level.

6 ft

Step-by-step explanation:

As we know that, the arch meet the ground are the value of x when y = 0

y=−0.9(x+3)(x−3)

<=> 0 = −0.9(x+3)(x−3)

<=> x=3 or x=-3  

So we have 2 coordinates: (3, 0) and (-3,0) and the distance between them is:

3 -(-3) = 6

=> The width of the arch at ground level is 6 ft