Give an efficient method by which Jim can determine at which gas stations should he stop.?

I'm not a programmer but I will tell you this: You're missing vital info, such as Gas consumption (MPG) then the difference in terrain when Jimmy reaches the Rocky Mountains. Computers will work on a 2 dimensional plane when in reality it's 3. This puts strain on the engine and lowers the MPG. And 'n' hasn't changed at all even when you travel 500 miles. You'll be stopping when your starting causing a serious loop or lockup. "n's" should be labeled diferent from one another na, nb, nc, etc... A computer can help you calculate possibilities but it can't drive a car in the similar fashion as a human. Look at traffic jams. Not all computers can culculate when they start or end. They just are.