$A$ person can swim in still water at $4 \, km/h$. If the speed of the water current is $2 \, km/h$,how many hours will the man take to swim back against the current for $6 \, km$?

$A$ 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.

$A$ 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......$km/h$.

Twice the speed downstream is equal to thrice the speed upstream. The ratio of the speed in still water to the speed of the current is:

The current of a stream runs at $1 \, km/h$. $A$ motor boat goes $35 \, km$ upstream and back again to the starting point in $12 \, hours$. The speed of the motor boat in still water in $km/h$ is:

$A$ man can row upstream $36 \text{ km}$ in $6 \text{ hours}$. If the speed of a man in still water is $8 \text{ km/hr}$,find how much distance he can cover downstream in $10 \text{ hours}$? (in $\text{km}$)