5/3 = 1/4 mile every 1 2/3 minutes
1 mile = 1 2/3 * 4 = 6 2/3 minutes
3 miles x 6 2/3 = 20 minutes total for Laurine
5/7 = 1/10 mile every 0.714 minutes
0.714 *10 = 7.14 minutes per mile
7.14*3 = 21.42 minutes total for Anna
21.42 - 20 = 1.42 minutes = 1 minute 25 seconds faster