Ratio of speed of a boat in still water to speed of stream is $9:2$. The boat travels a distance of $(\mathrm{D}+40) \mathrm{km}$ downstream and $\mathrm{D} \mathrm{km}$ upstream. If the ratio of time taken by the boat to travel upstream and downstream is $4:3$, respectively, then find the value of $\mathrm{D}$?

Ratio between speed of boat in still water to speed of stream is $8:1$.If $67.5$ kms is travelled downstream in $2.5$ hours then find the difference between speed of boat in still water to speed of stream?

Quantity $1$: Ratio between the speed of the boat in still water to the speed of the stream is $2:1$. Total time taken by a man to cover distance of $72$ km in upstream and comeback is $32$ hours. Find downstream speed.

Quantity $2$: $9$ $9 \mathrm{km}/\mathrm{h}$.

A boat in still water takes $15$ hours to reach its destination and come back from there. In the same river, it takes $16$ hours for the same journey where there is a current in the water. The difference between the speed of the boat and the river current is $15$ $km/hr$. Find out the speed of the river?

Speed of a boat along with the current and against the current are $12$ km/hr and $6$ km/hr respectively. What is the speed of the boat (in km/hr) in still water?