You could, if you wished, find the rate (speed): speed = distance / time.
Here, speed = (24 miles) / (6 minutes) = 4 miles / min.
Then, multiply (4 miles / min) by (6 minutes). Answer: 24 miles.
The fastest way is that proposed by the other person who answered this question: You can get your answer directly from the problem statement without having to do any work.
Are you certain that you have copied down this problem correctly? Do you realize that 4 miles / min is 240 miles per hour?