SOLUTION: Jack and his dad went canoeing to earn one of the merit badges Jack needed for Scouts. They paddled upstream for 16miles and it took them 4 hrs. After a short rest, they made the r

Let "u" be the rate of the canoe in still water (in miles per hour),

and let "v" be the rate of the current.


Then the effective speed canoeing upstream is


    u - v =  = 4   miles per hour   (1)


while the effective speed canoeing downstream is 


    u + v =  = 8   miles per hour (2)


Thus you have this system of two equations in 2 unknowns


    u - v = 4,      (1')

    u + v = 8.      (2')


To solve the system, add the equations (1') and (2').  You will get


    2u = 4 + 8 = 12,   which implies  u = 12/2 = 6 miles per hour.


Thus the rate of the canoe in still water is 12 miles per hour.


The from equation (2') ,  v = 8-u = 8-6 = 2.


Thus the rate of the current is 2 miles per hour.