$A$ boat goes $13\, km$ upstream in $39\, minutes$. The speed of the stream is $3\, km/h$. The speed of the boat in still water is......$km/h$.

$A$ person can row with the stream at $8 \text{ km/h}$ and against the stream at $4 \text{ km/h}$. The speed of the current is (in $\text{km/h}$):

$A$ man can row $40\, km$ upstream and $55\, km$ downstream in $13\, hours$. Also,he can row $30\, km$ upstream and $44\, km$ downstream in $10\, hours$. Find the speed of the man in still water and the speed of the current.

$A$ man rows upstream $12 \text{ km}$ and downstream $28 \text{ km}$,taking $5 \text{ hours}$ each time. The velocity of the water current is ......... $\text{km/h}$.

$A$ boat running upstream takes $8$ $hours$ $48$ $minutes$ to cover a certain distance,while it takes $4$ $hours$ to cover the same distance running downstream. What is the ratio between the speed of the boat and speed of the current respectively?

$A$ 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?