Question

A boat goes 40 km upstream in 8 hrs and 36 km downstream in 6 hrs. What is the speed of the boat in still water?

Answer 1

so we can make a picture

Answer 2

Sure

Answer 3

Let
x = speed of boat in still water
y = current of water

Using

distance = rate * time

40 = (x - y) * 8
36 = (x + y ) *6

Answer 4

Yeah... Thats what I wanted...

so, they become:

x - y = 5
x + y = 6

and solving them x = 5.5 and y = 0.5

Thanks a lot @perl