Lydia drove 216 miles and used 6 gallons of gasoline on a recent trip. Which of the following represents the unit rate of gasoline used on this trip?
a3 miles per gallon
b.3 miles per gallon
c.36 miles per gallon
d.36 miles per gallon
e.210 miles per gallon
f.210 miles per gallon
g.222 miles per gallon