If a Rocket Is Fired Vertically into the Air with a Speed

Multiple Choice

If a rocket is fired vertically into the air with a speed of feet per second, its height at time t seconds is given by . Here is a graph of its height at various times, with the details left out. How long will the rocket be in the air? ( Hint : How high is it when it hits the ground?)

A) 20 seconds
B) 16 seconds
C) 24 seconds
D) 15 seconds
E) 14 seconds