To determine how far the firework will travel before it reaches the ground, we need to solve the quadratic equation given by the height function, which is set to zero:
\[ 0 = -x^2 + 15x. \]
This can be rearranged into standard quadratic form:
\[ -x^2 + 15x = 0. \]
Factoring out an \(x\):
\[ x(-x + 15) = 0. \]
Setting each factor equal to zero gives us:
- \(x = 0\) (which represents the starting point of the firework),
- \(-x + 15 = 0 \Rightarrow x = 15\) (the distance traveled before it hits the ground).
Thus, the firework will travel 15 feet before it reaches the ground.
So, the correct response is:
15 feet.