You are driving to a vacation spot that is 1500 miles away. Including rest stops, it takes your 42 hours to get to vacation spot. You estimate that you drove at an average speed of 50 mph. How many hours were you not driving?

The answer is 12.

Since it took 42 hours to arrive at the vacation, and you were driving 50 miles per hour, the number of miles you would have driven (if you were driving nonstop) would be 2100. But since the mileage was only 1500, we subtract 1500 from 2100 getting 300. and dividing 300 by 50, we arrive at 12.