Lynne was the one who ran farther and by 7/8 miles
you can see Lynne ran further because she was running 3 whole miles while Shelly was only running 2 whole miles,then you have to subtract to see how much more Lynne ran .
You found a common denominator between 8 and 4. 4 can turn into 8. so you multiply 4x2 and add 8=1 to get a mixed number of 2 2/8. Now you have to turn 3 1/8 into fraction because you cannot subtract 2 1/4 from 3 1/8. You can turn the fraction into 18/8 and 25/8.
Shelly ran 18/8 miles
Lynne 25/8 miles
Lynne ran 25/8 -18/8= 7/8 miles
further than Shelly