Answer:
After 11 seconds the hovercraft will land on ground
Explanation:
Given function that shows the height of a hovercraft,
![h(x) = -(x-11)(x+3)](https://img.qammunity.org/2020/formulas/mathematics/high-school/fzs558xw1mfit8sg9ljyecdg8r7pdd5tea.png)
Where,
x = number of second.
When the hovercraft land the ground,
![h(x) = 0](https://img.qammunity.org/2020/formulas/mathematics/high-school/ya5d5ayofyimekxxlw9fcoeqxq37qg9qkt.png)
![-(x-11)(x+3)=0](https://img.qammunity.org/2020/formulas/mathematics/high-school/tbn1rpwz8f48d5ftdhqdkgulhwyuarooty.png)
![\implies (x-11)(x+3)=0](https://img.qammunity.org/2020/formulas/mathematics/high-school/7wp61nz4uaygkrq02bpy96oh8lh4qfqbj9.png)
By zero product property,
x - 11 = 0 or x + 3 = 0
⇒ x = 11 or x = -3 ( not possible ),
Hence, after 11 seconds the hovercraft will land on ground.