120 miles on 8 gallons of gas....120/8 = 15 miles per gallon
435/15 = 29 gallons <==
or u can do it this way...
120 / 8 = 435 / x....120 miles to 8 gallons = 435 miles to x gallons
cross multiply
(120)(x) = (435)(8)
120x = 3480
x = 3480/120
x = 29 <==
either way, u should get the same answer