Put a cuboid iron block in a cylindrical container with a bottom radius of 4dm. Now turn on the faucet and fill the container with water. After 3 minutes, the water surface just covers the top surface of the cuboid. After another 18 minutes, the water just fills the container. The container is known. The height is 50cm and the height of the cuboid is 20cm. Find the volume of the cuboid.
一个底面半径为4dm的圆柱形容器内放一个长方体铁块，现打开水龙头往容器内灌水，3分钟时水面恰好没过长方体的顶面，再过18分钟水正好灌满容器，已知容器的高为50cm，长方体的高是20cm．求长方体的体积．
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">50 - 20</gadget>
<output>30</output>

<gadget id="calculator">20 / 30</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>

<gadget id="calculator">20 / 10</gadget>
<output>2</output>

<gadget id="calculator">3.14 * 16 * (3/4) * 2</gadget>
<output>75.36</output>

<result>75.36</result>