$A$ man can row at the rate of $4 \text{ km/hr}$ in still water. If the time taken to row a certain distance upstream is $3$ times as much as to row the same distance downstream,find the speed of the current in $\text{km/hr}$.

The speed of a boat in still water is $4 \, km/h$ and the speed of the current is $2 \, km/h$. If the time taken to reach a certain distance upstream is $9 \, hours$,find the time it will take to go the same distance downstream (in $hrs$).

Rohit can row a certain distance downstream in $8$ $hours$ and return the same distance in $12$ $hours$. If the stream flows at the rate of $5$ $km/hr$,find the speed of Rohit in still water (in $km/hr$).

$A$ man can row against the current $\frac{3}{4}$ of a kilometre in $15$ minutes and returns the same distance in $10$ minutes. The ratio of his speed to that of the current is

$A$ boatman goes $2\, km$ against the stream in $1\, hour$ and goes $1\, km$ along the current in $10\, minutes.$ How long will he take to go $5\, km$ in stationary water?

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