$A$ swimmer's speed in downstream is $11 \, km/h$ and speed of the stream is $1.5 \, km/h$. Find the upstream speed of the swimmer? (in $km/h$)

$A$ man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat (in still water) and the stream is:

In a river flowing at $2\, km/h$, a boat travels $32\, km$ upstream and then returns downstream to the starting point. If its speed in still water is $6\, km/h$, find the total journey time in hours.

$A$ 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 $km/h$).

$A$ boat takes $3$ $hours$ to travel from place $M$ to $N$ downstream and back from $N$ to $M$ upstream. If the speed of the boat in still water is $4$ $km/h$,what is the distance between the two places? (in $km$)

$A$ 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 $km$)