Question 933082
Let 80 miles = the distance Mr. Paddle traveled
        4hrs = the duration of the boat traveled on downstream
        8hrs = the duration of the boat traveled on upstream

Mr. paddle took his boat 80 miles down a river and back. The trip downstream took 4hrs while back took 8hrs.

Distance = (rate)(time)
rate     =  Distance/time

     80  = (x+y)4
     10  =  x+y
     80  = (x-y)8
     20  =  x-y

x+y = 20
x-y = 10
 2x = 30
  x = 15

Substitute x with 15
15+y = 20
   y = 5
15-y = 10
   y = 5

The boat's speed is 15kph while the current's speed is 5kph.