Answer: If the train moves a constant speed of 8 miles for every 6 minutes then if the time where to be 3 minutes you would have to divided 2 and 8 because the time was split in half you would also have to split the 8 as well. Now if the time was 15 minutes you would have to add more since 6 got 9 more you will have to add 9 more to 8.
