rate of motorboat: b
rate of current: c
So the rate the boat travels upstream is $b - c$, and the rate it travels downstream is $b + c$
[tex]d = rt[/tex]
[tex]200 = (b - c)\cdot 5[/tex]
[tex]200 = (b + c)\cdot 4[/tex]
[tex]b - c = 40[/tex]
[tex]b + c = 50[/tex]
Adding these equations, we get:
[tex]2b = 90[/tex]
[tex]b = 45[/tex]
So
[tex]c = 50 - 45 = 5[/tex]
Therefore the rate of the boat is 45kph, and the rate of the current is 5kph
Hope this helps :)
