$A$ boat covers a certain distance downstream in $1 \text{ hour}$,while it comes back in $1.5 \text{ hours}$. If the speed of the stream is $3 \text{ km/hr}$,what is the speed of the boat in still water? (in $\text{km/hr}$)

$A$ boat goes $24 \, km$ upstream and $28 \, km$ downstream in $6 \, hours$. It goes $30 \, km$ upstream and $21 \, km$ downstream in $6 \, hours$ and $30 \, minutes$. The speed of the boat in still water is $...... \, km/hr$.

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

On a river,$Q$ is the midpoint between two points $P$ and $R$ on the same bank. $A$ boat can travel from $P$ to $Q$ and back in $12$ hours,and from $P$ to $R$ in $16$ hours $40$ minutes. How long would it take to travel from $R$ to $P$? (in hours)

The speed of a boat in still water is $10\, km/hr$. If it can travel $26\, km$ downstream and $14\, km$ upstream in the same time,the speed of the stream is.....$km/hr$.

Twice the speed downstream is equal to thrice the speed upstream. The ratio of the speed in still water to the speed of the current is: