$A$ boat can travel with a speed of $13\, km/hr$ in still water. If the speed of the stream is $4\, km/hr,$ find the time taken by the boat to go $68\, km$ downstream. (in $hours$)

If a boat goes upstream at a speed of $21\, km/h$ and comes back the same distance at $28\, km/h$,what is the average speed (in $km/h$) for the total journey?

$A$ boat goes $6\, km$ upstream and back again to the starting point in $2\, hours$. If the velocity of the stream is $4\, km/hr$,what is the speed of the boat in still water? (in $km/hr$)

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 $\%$)

Speeds of a boat along the current and against the current are $10 \ km/hr$ and $8 \ km/hr$ respectively. What is the speed (in $km/hr$) of the current?

$A$ person takes total $5$ $hours$ to go to a destination downstream and come back upstream by boat. If the speed of the boat in still water is $10 \text{ km/h}$ and the speed of the stream is $4 \text{ km/h}$,what is the distance of the destination from the starting point (in $\text{km}$)?