There may be a simpler way to do this but this worked:
Divide 4.5/30 you get 3/20
Divide 7/45 you get 7/45 (can't be simplified as a fraction)
To see which is larger, you have to find a common denominator. There might have been another one but I just chose to multiply them together. So you get 3/20=135/900 and 7/45=140/900 So Brittany went slower by 3/20 mile per minute.
Hope that helps. Feel free to ask questions if that doesn't make sense.
