Someone please explain

Question

A toy rocket travels at an initial velocity of 144 feet per second. The height of the rocket can be modeled by the function ℎ(𝑡) = 144𝑡 − 16𝑡^2 , where t is the time in seconds. When will the rocket return to the ground?

Answer 1

The rocket will return to the ground when h(t)=0 for t>0, i.e. 16t=144 and t=9.