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

$A$ boatman rows $1\, km$ in $5\, min$ along the stream and $6\, km$ in $1\, h$ against the stream. The speed of the stream is in $km/h$:

$A$ person can row a certain distance downstream in $6$ hours and return the same distance in $9$ hours. If the stream flows at the rate of $3$ $km/h$,find the speed of the person in still water (in $km/h$).

$A$ boat moves downstream at the rate of $1 \, km$ in $10 \, minutes$ and upstream at the rate of $4 \, km/h$. What is the velocity of the current (in $km/h$)?

$A$ 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......$km$.

$A$ swimmer covers a distance of $28\, km$ against the current and $40\, km$ in the direction of the current. If in each case he takes $4\, hours$,then the speed of the current is..........$km/h$.