First, lets convert 21 km to m, km to m is moving the point to the left three times. So 21km = 21000m
Second, let's convert 15 mile to m, 1 mile is equal to 1609.34 meters, so 15 x 1609.34 = 24140.2 meters.
Third, Zale run 21000 meters while Enzo run 24140.2 meters.
Enzo run farther than Zale.