1st way:
When Luis travels 216 mi, he will use :
1) minivan - 216 mi*18 gal/1 mi = 216*18 gal
2) compact - 216 mi/24 mi/gal = 216*24 gal
He will save 216*24 - 216*18 = 216(24 -18)= 1296 gal
2d way.
For 1 mi he saves 24 -18 = 6 gallons
For 216 mi he saves 216*6 = 1296 gal
