$A$ boat travels upstream from $B$ to $A$ and downstream from $A$ to $B$ in $3$ $hrs$. If the speed of the boat in still water is $9$ $km/h$ and the speed of the current is $3$ $km/h$,the distance between $A$ and $B$ is......$km$.

$A$ boat goes $2\, km$ upstream and $3\, km$ downstream in $20$ minutes. It goes $7\, km$ upstream and $2\, km$ downstream in $53$ minutes. What is the speed (in $km/hr$) of the boat in still water?

Rahul can travel $12 \text{ miles}$ downstream in a certain river in $6 \text{ hours}$ less than it takes him to travel the same distance upstream. But if he could double his usual rowing rate for his $24 \text{ mile}$ round trip,the downstream $12 \text{ miles}$ would take only one hour less than the upstream $12 \text{ miles}$. What is the speed of the current in $\text{miles/hour}$?

From the given statements,decide which of the statement$(s)$ is/are necessary to answer the question.
What is the speed of a train?
$I.$ The length of the train is $240 \ m$.
$II.$ The train crosses a pole in $24 \ s$.
$III.$ The train crosses a platform in $48 \ s$.

$A$ boat travels $32 \ km$ downstream in $4 \ hours$ and $24 \ km$ upstream in $6 \ hours$. What is the speed (in $km/hr$) of the boat in still water?

$A$ man can row at the rate of $3.5 \, km/h$ in still water. If the time taken to row a certain distance upstream is $2 \frac{1}{2}$ times as much as the time taken to row the same distance downstream,find the speed of the current in $km/h$.