The speed of a boat in still water is $8\, km/h$. If its speed downstream is $15\, km/h$,then the speed of the stream is $.......\, km/h$.

$A$ boat covers a certain distance downstream in $2$ $hours$,but takes $4$ $hours$ to return upstream to the starting point. If the speed of the stream is $3$ $km/h$,find the speed of the boat in still water (in $km/h$).

$P$,$Q$,and $R$ are three towns on a river that flows uniformly. $Q$ is equidistant from $P$ and $R$. $I$ row from $P$ to $Q$ and back in $10$ $hours$,and $I$ can row downstream from $P$ to $R$ in $4$ $hours$. Compare the speed of my boat in still water with that of the river.

In a stream running at $2 \ km/h$,a motorboat goes $6 \ km$ upstream and back again to the starting point in $33 \ minutes$. Find the speed of the motorboat in still water. (in $km/h$)

$A$ man can row $6\, km/h$ in still water. If the river is running at $2\, km/h$,it takes $3\, hours$ more to row upstream than to row downstream for the same distance. How far is the place? (in $km$)

$A$ boat travels $60$ km downstream and $20$ km upstream in $4$ hours. The same boat travels $40$ km downstream and $40$ km upstream in $6$ hours. What is the speed (in $km/hr$) of the stream?