Math word problem

Question

A motorboat takes 5 hours to travel 200 km going upstream. The return trip takes 4 hours going downstream. What is the rate of the boat in still water and what is the rate of the current?

Answer 1

when we say up stream and downstream, that means respectively the speed of the stream is subtracted and added to the speed of the boat. also the assumption is that the speed of water stream and the boat is constant.

also we know that for constant velocity motion x=vt therefore

(vb+vs)*4=200

(vb-vs)5=200 where vb is boat velocity and vs is stream velocity

the answer from here is easy, its just two equations two unknowns.