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
L= 3w
2(3w + w) = 112
6w + 2w = 112
8w = 112
W= 14
The greatest possible value for width is 14