$A$ boat covers $24 \text{ km}$ upstream and $36 \text{ km}$ downstream in $6 \text{ hours}$,while it covers $36 \text{ km}$ upstream and $24 \text{ km}$ downstream in $6 \frac{1}{2} \text{ hours}$. The velocity of the current is .... $\text{km/h}$.

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 moves $20 \, km$ downstream in $5 \, hours$ and $10 \, km$ upstream in the same time. The speed of the stream is...........$km/h$.

Speed of a boat in standing water is $9 \text{ km/h}$ and the speed of the stream is $1.5 \text{ km/h}$. $A$ man rows to a place at a distance of $105 \text{ km}$ and comes back to the starting point. The total time taken by him is (in $\text{ hours}$)

$A$ man can row $6 \, km/h$ in still water. If the speed of the current is $2 \, km/h$,it takes $3 \, h$ more in upstream than in the downstream for the same distance. The distance is......$km$.

$A$ man can swim $3 \text{ km/h}$ in still water. If the velocity of the stream is $2 \text{ km/h}$,the time taken by him to swim to a place $10 \text{ km}$ upstream and back is (in hours):