Slowly but surely

When I calculate proportions, I still do so the way Mrs. Lovell taught me in seventh-grade algebra: I write an equation with a variable, and then one under that, and then one under that. I am, you see, solving for the variable.

Just now, for example, I was trying to figure out how many gallons of gas a 327-mile road trip would consume, given that my truck gets 22 miles to the gallon. I wrote this:

327 mi/x = 22 mi/1 gal
327 = 22x
x = 327/22
x = 14.86 gal

I get the sense that sharper minds than mine can figure out what to divide by which without having to write columns of equations. But I never had much of a head for figures. After 22 years, am I permanently stuck in the seventh grade?