When the speed of a boat in still water is $4\, km/h$ and the rate of stream is $2\, km/h$,find the upstream speed of the boat (in $km/h$).

$A$ boatman can row $2\, km$ against the stream in $20\, minutes$ and return in $18\, minutes.$ Find the rate of the current in $km/h$.

$A$ boat goes $14 \ km$ upstream in $42 \ minutes$. The speed of the stream is $4 \ km$. The speed of the boat in still water is .......... $km/h$.

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 goes $24 \, km$ upstream and $28 \, km$ downstream in $6 \, hours$. It goes $30 \, km$ upstream and $21 \, km$ downstream in $6 \, hours$ and $30 \, minutes$. The speed of the boat in still water is $...... \, km/hr$.

$A$ 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.