In a cylindrical bucket, the diameter of the bottom surface is 20cm. A cylindrical iron block with a radius of 5cm is completely put into the water. The height of the water surface in the bucket is 9cm. If the iron block in the water is taken out, the water in the bucket will drop by 4cm. What is the volume of this iron block?
一个圆柱形水桶里，底面直径20cm，把一段半径5cm的圆柱形铁块完全放入水中，桶里的水面高度为9cm，如果把水中的铁块拿出来后，桶里的水就下降4cm．这铁块的体积是多少？
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100 * 4</gadget>
<output>1_256</output>

<result>1_256</result>