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I am a little perplexed on how to answer this problem, I got an answer, but it doesn't seem to fit within the context of the problem. I don't know if it is because I am using the wrong equation, or if I am just plugging the numbers in wrong:

A rocket is fired vertically upward with an initial velocity of 80.0 m/s. It accelerates upward at 4.00 m/s^2 until it reaches an altitude of 1000 m. At that point, its engines fail and the rocket goes into free flight, with an acceleration of -9.8 m/s^2. (a) How long is the rocket in motion? (b) What is its maximum altitude? (c) What is its velocity just before it collides with the earth?

Also, I was wondering if someone would mind checking this problem for me:

The Height of a helicopter above the ground is given by h=3.00t^3, (h is in m., t is in s.) After 2.00 s, the helicopter releases a small mailbag. How long after its release does the mailbag reach the ground?

3(2)^2=24m.

24m.=0m.+(0m/s)t+1/2(9.8m/s^2)t^2

*t=2.21s.*

Thanks for the help!!