To find out how far the firework will travel before it reaches the ground, we need to solve the equation:
\[ 0 = -x^2 + 15x \]
First, we can rearrange the equation:
\[ -x^2 + 15x = 0 \]
Factoring out an \( x \):
\[ x(-x + 15) = 0 \]
This gives us two potential solutions:
- \( x = 0 \)
- \( -x + 15 = 0 \) which simplifies to \( x = 15 \)
Thus, the firework will reach the ground when \( x = 15 \) feet.
The correct answer is:
15 feet