how can the time delay between lightening and thunder be used to tell how far away a storm is?

Question: how can the time delay between lightening and thunder be used to tell how far away a storm is?
- Keywords:
  distance,
  lightening,
  storm,
  thunder
Asked by thing2oxo to Ed, Hayley, Jason, Nathan, Sophie on 15 Mar 2013.
- Jason King answered on 15 Mar 2013:
  
  This is because light and sound travel at different speeds. Light is really fast, so you see the lightening pretty much immediately, but sound only travels at about 300m/s. That means that if the lightening was 900m away, it would take 3 seconds for the sound of the thunder to get to you. The longer the delay, the further away the storm must be.

Question: how can the time delay between lightening and thunder be used to tell how far away a storm is?