To determine how far the firework will travel before it reaches the ground, we need to solve the equation \(0 = -x^2 + 15x\).
We can rewrite this as: \[ -x^2 + 15x = 0 \]
Factoring the equation gives us: \[ x(-x + 15) = 0 \]
Setting each factor to zero, we get:
- \(x = 0\) (this represents the starting point)
- \(-x + 15 = 0\) which simplifies to \(x = 15\)
Thus, the firework will reach the ground at \(x = 15\) feet.
The answer is 15 feet.