A cuboid iron block is placed in a cylindrical container. Now pour water into the container for 3 minutes, and the water just covers the top surface of the iron block; after another 18 minutes, the container is filled with water. It is known that the height of the container is 50 cm, and the height of the cuboid is is 20 centimeters, what fraction of the area of the bottom surface of the cuboid is that of the cylindrical container?
圆柱形容器内装一个长方体铁块，现向容器内注水3分钟，水恰好没过铁块顶面；又过了18分钟，容器内注满水，已知容器的高是50厘米，长方体的高是20厘米，则长方体底面面积是圆柱形容器的几分之几？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">18 * (2/3)</gadget>
<output>12</output>

<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<gadget id="calculator">9 / 12</gadget>
<output>3/4 = around 0.75</output>

<result>3/4 = around 0.75</result>