A barge takes 4 hours to move (at a constant rate) downstream for 32 miles,
helped by a current of 2 miles per hour. If the barge's engines are set at the
same pace, find the time of its return trip against the current.

It went 32 miles downstream in 4 hours, so it traveled downstream 8 mph.  The
current helped it along by 2 mph, so the barge would have gone 6 mph if it had
been in still water.  Then on the return trip the current would slow the barge
down to 4mph, so it would take it 8 hours to make the 32 mile return trip at 
4 mph.

You don't really need algebra to do the problem, as you can do it in your head.

Edwin
AnlytcPhil@aol.com