Ahovercraft takes off from a platform. its height (in meters), xxx seconds after takeoff, is modeled by: h(x)=-3(x-3)^2+108 how many seconds after takeoff will the hovercraft land on the ground?

For this case we have the following function:

By the time of the landing we have:

From here, we clear the value of x.

We have then:

Discarding the negative root we have:

9 seconds after takeoff the hovercraft will land on the ground