Answer:
I believe it is 20 minutes.
Explanation:
It takes 1 hour for Danielle to run 3 miles ahead of David. You would have to divide 3 hours by 3 which is 1 mile. You have to do the same for the time it took to run 3 miles ahead (1 hour). 1 hour = 60 minutes and 60 divided by 3 is 20. This means it should take Danielle 20 minutes to be 1 mile ahead of David.
Hope this explanation helps!