What time will be taken by a boat to cover a distance of $128\, km$ along the stream,if the speed of a boat in still water is $24\, km/h$ and the speed of the stream is $8\, km/h$? (in $h$)

$A$ 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 ......... $\text{km/h}$.

$A$ motorboat travelling at some speed can cover $25\, km$ upstream and $39\, km$ downstream in $8\, h$. At the same speed,it can travel $35\, km$ upstream and $52\, km$ downstream in $11\, h$. The speed of the stream is........$km/h$.

$A$ boat takes $3$ $hours$ to travel from place $M$ to $N$ downstream and back from $N$ to $M$ upstream. If the speed of the boat in still water is $4$ $km/h$,what is the distance between the two places? (in $km$)

$A$ boatman goes $2\, km$ against the current of the stream in $1\, h$ and goes $1\, km$ along the current in $10\, min.$ How long will he take to go $5\, km$ in stationary water?

$P, Q, R$ are three towns on a river which flows uniformly. $Q$ is equidistant from $P$ and $R$. $A$ man rows from $P$ to $Q$ and returns in $10 \, h$. He can row from $P$ to $R$ in $4 \, h$. The ratio of the speed of the man in still water to the speed of the current is