18 / 1 = x / 15......18 miles to 1 gallon = x miles to 15 gallon
cross multiply
(1)(x) = (18)(15)
x = 270 miles
I believe the answer is a.
You add up all of the sides and the numbers that are there you pretend that they are on the other side and just add all of them up correctly and you will get your answer.
Do 10 to the sixth power first then multiply that by 7 you use PEMDAS