Solving a Helicopter Height Equation

[rokas]

Homework Statement

The height of a helicopter is given by h=3.00t^3, where h is in meters and t in seconds. After 2s, the helicopter releases a small bag. How long does it take for the bag to reach the ground?

Xi = 0
Xf = 24 (i got 24 meters when i plugged in seconds in h=3.00t^3)
A(gravity) = 9.81
Vi = 0

Homework Equations

Xf=Xi+Vi(t)+1/2at^2

The Attempt at a Solution

i plugged in the numbers

24=(t)+1/2(9.81)(t^2)
24=(t)+4.905(t^2)
19.095=t^3

this is where i am stuck because i don't know how to solve an equation with a letter cubed...
i don't know if I am doing this right, help?

 

[rl.bhat]

Helicopter rising. Its initial velocity in the upward direction is given by dh/dt. Find vi at 2 seconds.
Initial height from the ground xo =24 m. Final height xf = 0. Find t.