To convert a mixed number into a fraction, you first have to turn the whole number into a fraction with the same denominator, and then add the two together.
4 will become 20/5, because 5 x 4 = 20 (5/5 = 1, so 20/5 = 4)
20/5 + 3/5 = 23/5
The improper fraction is 23/5 miles.
I'm not completely sure by what you mean by "a fraction greater than one," but I'm assuming you mean an improper fraction.
