A cylindrical cistern has a bottom diameter of 20 meters and a depth of 2 meters. After the water is stored, the water depth is 1.8 meters. If you want the water surface to rise to 1.85 meters, how many cubic meters of water need to be injected?
一个圆柱形蓄水池，底面直径20米，深2米．蓄水后，水深1.8米，如果想要水面上升至1.85米，还需要注入多少立方米的水？
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

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

<gadget id="calculator">1.85 - 1.8</gadget>
<output>0.05</output>

<gadget id="calculator">3.14 * 100 * 0.05</gadget>
<output>15.7</output>

<result>15.7</result>