The hourglass is a timekeeping tool in ancient my country. Its shape is a combination of two identical conical containers. The bottom of the hourglass below has a radius of 5cm and a height of 9cm. It is now filled with sand. If the flow rate of the sand is 7.85 cubic meters cm/sec. How long does it take for all the sand to flow from above to below?
沙漏是我国古代的一种计时工具，形状是两个完全相同的圆锥形容器的组合体，下面这个沙漏的底面半径是5cm，高是9cm，现在装满了沙子，如果沙子的流速是7.85立方厘米/秒．沙子从上面全部流到下面需要多长时间？
<gadget id="calculator">235.5 / 78.5</gadget>
<output>3</output>

<result>3</result>