To determine how far the firework will travel before it reaches the ground, we need to solve the quadratic equation:
\[ 0 = -x^2 + 15x \]
First, we can factor out an x:
\[ 0 = x(-x + 15) \]
Setting each factor equal to zero gives us:
- \( x = 0 \)
- \( -x + 15 = 0 \) which simplifies to \( x = 15 \)
The two solutions indicate that the firework will be at ground level (height 0) at \( x = 0 \) feet (when it is shot) and at \( x = 15 \) feet when it comes back to the ground.
Thus, the firework will travel 15 feet before it reaches the ground.
The correct response is: 15 feet.