SOLUTION: Janet and Michael took a canoeing trip, traveling 6 miles upstream along a river, against a 2 mi/h current. They then returned downstream to all the starting point of their trip. I

Let x be the rate of the canoe in still water.


Then the effective rate upstream is (x-2) miles per hour, and the time upstream is   hours.


The effective rate downstream is (x+2) miles per hour, and the time downstream is   hours.


So, your time equation is


     +  = 4.


Multiply both sides by (x-2)*(x+2). You will get


    6*(x+2) + 6*(x-2) = 4*(x-2)*(x+2)


    6x + 12 + 6x - 12 = 4(x^2 - 4)

    12x = 4x^2 - 16


    4x^2 - 12x - 16 = 0


    x^2 - 3x - 4 = 0

    (x-4)*(x+1) = 0.


Only positive root x= 4 is meaningful.


Answer.  The rate of the canoe in still water is 4 miles per hour.