If you are traveling 543 miles and you know that your car gets 18 miles per gallon of gasoline, approximately how many gallons of gasoline will you need for a one-way trip?

we know that

the car gets 18 miles per > 1 gallon of gasoline

so

for 543 miles > x gallons of gasoline

by proportion

543/18=x/1>x=543/18>x=30.17 gallons

therefore

the answer is

30.17 gallons