I got -19/655 and i know for sure this isnt the correct answer.
18 / 1 = x / 15......18 miles to 1 gallon = x miles to 15 gallon
cross multiply
(1)(x) = (18)(15)
x = 270 miles
Check the picture below.
make sure your calculator is in Degree mode.
You do 90-45 bc the whole angel must equal 90