If the speed of a swimmer in still water is $9\, km/h$,find the downstream speed of the swimmer when the river is flowing with a speed of $6\, km/h$ (in $km/h$).

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

The speed of a boat downstream is $\frac{16}{9}$ times the speed of the boat upstream. The speed of the current is what percent of the speed of the boat in still water? (in $\%$)

$A$ man swimming in a stream which flows at $1 \frac{1}{2} \text{ km/h}$ finds that in a given time he can swim twice as far with the stream as he can against it. At what rate does he swim? (in $\text{km/h}$)

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 $hrs$).

$A$ 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 $6.5 \text{ hours}$. The velocity of the current is ......... $\text{km/h}$.