$A$ man can row $15\, km/h$ downstream and $9\, km/h$ upstream. The speed of the boat in still water is.....$km/h$

$A$ man moves downstream at a rate of $14\, km/h$ and upstream at a rate of $6\, km/h$. The speed of the boat in still water is........$km/h$.

$A$ river is flowing at a speed of $5\, km/h$ in a particular direction. $A$ man,who can swim at a speed of $20\, km/h$ in still water,starts swimming along the direction of flow of the river from point $A$ and reaches another point $B$ which is at a distance of $30\, km$ from the starting point $A$. On reaching point $B$,the man turns back and starts swimming against the direction of flow of the river and stops after reaching point $A$. The total time taken by the man to complete his journey is:

If a man's rate with the current is $12 \text{ km/h}$ and the rate of the current is $1 \frac{1}{2} \text{ km/h}$,then his rate against the current is ...... $\text{km/h}$.

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:

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 $hrs$).