first divide 1 1/8 by 3/8 to see how many 3/8 distances you have, then multiply that by 15 to get total miles:
convert 1 1/8 into an improper fraction: 1 1/8 = 1 = 8/8 + 1/8 = 9/8
now divide 9/8 by 3/8 : 9 /3 = 3 8/8 = 1 = 3/1 = 3
you have 3 3/8 distances
each one is 15 miles so 15 x 3 = 45 miles
