To find out how far the firework will travel before it reaches the ground, we need to solve the equation:
\[ 0 = -x^2 + 15x. \]
This can be rearranged to:
\[ -x^2 + 15x = 0. \]
We can factor out \( x \):
\[ x(-x + 15) = 0. \]
Setting each factor equal to zero gives us:
- \( x = 0 \)
- \( -x + 15 = 0 \) which simplifies to \( x = 15 \).
The solutions to the equation are \( x = 0 \) and \( x = 15 \). The \( x = 0 \) solution indicates the starting point (when the firework is launched), and \( x = 15 \) represents the point where it will hit the ground.
Therefore, the firework will travel a distance of 15 feet before it reaches the ground.
Answer: 15 feet