Hello, sologuitar!

We are expected to be familiar with this formula: .A rocket loaded with fireworks is to be shot vertically upward from the ground level

with an initial velocity of 200 feet per second.

When the rocket reaches a height of 400 feeton its upward trip, the fireworks will be detonated.

How many seconds after liftoff will this take place?

. . where is the height of the rocket (in feet) seconds after liftoff.

When is ?

We have: .

. . which factors: .

. . and has roots: .

The fireworks will be detonated seconds after liftoff.