Ok this is what you do it went 12 miles and hour to travel the perimeter in 7.5 minuets there are 60 min in an hour do 12/60 thats 0.2 miles every min do 7.5x0.2=1.5 so the perimeter is 1.5 miles but you are looking for length so the length would be 0.5 because that mean the width would have to be 0.25 and
