Help w/ a physics problem

[Bradyams]

I need help with this quick problem. For some reason I can't figure it out.

Automobile Airbags: The human body can survive a negative acceleration trauma incident (sudden stop) if the magnitude of the acceleration is less than 250 m/s^2

If you are in an automobile accident with an initial speed of 108 km/h (30 m/s) and are stopped by an airbag that inflates from the dashboard, over what distance must the airbag stop you for you to survive the crash?

Thanks