It will take 8 minutes.
You use a proportion
5/1=2400/x you use 2400 because 2.4km=2400 meters and u need to use the same unit of measurement.
so cross multiplying gives you 5x=2400 which is equal to 480. BUT this is 48 seconds, and it asks you how many minutes, not seconds. So, you divide by 60 because there are 6 seconds in a minute, and you get 8.