$A$ man can row three-quarters of a kilometre against the stream in $11 \frac{1}{4}$ minutes. The speed (in $km/hr$) of the man in still water is

From the given statements,decide which of the statement$(s)$ is/are necessary to answer the question.
What is the speed of a boat in still water?
$I.$ The boat covers $12 \text{ km}$ in $2 \text{ hours}$ downstream.
$II.$ The boat covers the same distance in $4 \text{ hours}$ upstream.
$III.$ The speed of the stream is $\frac{1}{3}$ that of the boat in still water.

$A$ man can row $7\, km/hr$ in still water. If the river is running at $3\, km/hr$,it takes $6\, hours$ more to row upstream than to row downstream for the same distance. How far is the place? (in $km$)

$A$ motor-boat can travel at $10 \, km/h$ in still water. It travelled $91 \, km$ downstream in a river and then returned to the same place,taking altogether $20 \, hours$. Find the rate of flow of the river (in $km/h$).

$A$ motorboat travelling at some speed can cover $25\, km$ upstream and $39\, km$ downstream in $8\, h$. At the same speed,it can travel $35\, km$ upstream and $52\, km$ downstream in $11\, h$. The speed of the stream is........$km/h$.

$A$ boatman can row $2\, km$ against the stream in $20\, minutes$ and return in $18\, minutes.$ Find the rate of the current in $km/h$.