The ratio of the speed of a motorboat to the speed of the water current is $36: 5$. The boat travels along with the current in $5\, h\, 10\, min$. How long will it take to return?

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 $h$)

From the given statements,decide which of the statement$(s)$ is/are necessary to answer the question.
What is the speed of a boat in still water?
$I.$ The boat covers $12 \text{ km}$ in $2 \text{ hours}$ downstream.
$II.$ The boat covers the same distance in $4 \text{ hours}$ upstream.
$III.$ The speed of the stream is $\frac{1}{3}$ that of the boat in still water.

Rahul can travel $12 \text{ miles}$ downstream in a certain river in $6 \text{ hours}$ less than it takes him to travel the same distance upstream. But if he could double his usual rowing rate for his $24 \text{ mile}$ round trip,the downstream $12 \text{ miles}$ would take only one hour less than the upstream $12 \text{ miles}$. What is the speed of the current in $\text{miles/hour}$?

$A$ 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.

$A$ person can row with the stream at $8 \text{ km/h}$ and against the stream at $4 \text{ km/h}$. The speed of the current is (in $\text{km/h}$):