It is 150 miles away.Say how ???
I was travelling at 30mph at a rate of 20mpg, so I was using 1.5 gallons every hour for the driving itself.
I was also losing 0.5 gallon every hour. In total, I was using 2 gallons every hour.
Therefore to use all of the 10 gallons I started with, I travelled for 5 hours.
5 hours at 30mph is 150 miles. Hence, it was 150 miles away...!