If $2: x :: 5: 7$,then $x$ is equal to

Find the mean proportional between $9$ and $64$.

If $A: B = 2: 5$,$B: C = 4: 3$,and $C: D = 2: 1$,what is the value of $A: C: D$?

Two horses cost as much as $5$ dogs,$6$ dogs as much as $8$ oxen,$10$ oxen as much as $50$ sheep,$14$ sheep as much as $9$ goats. If the price of one goat is $Rs. 700$,find the cost of one horse (in $Rs.$).

Two candles of the same height are lighted at the same time. The first is consumed in $8 \text{ hours}$ and the second in $6 \text{ hours}$. Assuming that each candle burns at a constant rate,in how many hours after being lighted,the ratio between the height of the first and second candles becomes $2:1$?

Find a fourth proportional to the numbers $60, 48, 30$.