Question 83155
since the kayak goes one directions 2mph and the other direction 4 mph, it is known that the kayak goes twice the speed on the way back, so it takes half the time.  It is also known that the kayak is traveling for 6 hours.  Therefore, the kayak spends twice as much time going up than coming back.  

2x+x=6hours x=2
The kayak spends 2x, or 4 hours, going up and x, or 2, hours coming back

Traveling 4 hours at 2 mph will equal 8 miles
Traveling 2 hours at 4 mph will equal 8 miles

The kayak travels a total of 8 miles up the river and 8 miles back