One lap around 5he school track is 3/8 miles. Carin ran 31/2 laps. How far did she run?

Total distance is the distance per lap times the number of laps. (Note the units of "lap" cancel, leaving miles as the unit of the result.)

(3/8 mi/lap) * (3 1/2 lap) = (3/8) * (7/2) mi = 21/16 mi = 1 5/16 mi