A boat moves at a rate pf 12 mph in still water. If the river's current flows at a rate of 5 mph, how long does it take the boat to travel 31 miles upstream?
Use exactly the same reasoning as in the answer to your question after this one. Make sure you change the numbers!. If you don't make any mistakes, you should get 4 3/7 hours, or about 4 hours and 26 minutes.