A circular iron rod with a base radius of 2 cm is completely submerged in a cylindrical bucket. The water level rises by 4 cm. If the iron rod is pulled vertically out of the water by 9 cm, the water level falls by 3 cm. Find the volume of the iron rod.
把一根底面半径是2厘米的圆形铁棒全部浸没在圆柱形水桶中，水面上升4厘米，如果把铁棒竖着拉出水面9厘米，水面就下降3厘米，求铁棒的体积．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4 * 12</gadget>
<output>150.72</output>

<result>150.72</result>