A cylindrical glass tank with a bottom diameter of 20 cm and a depth of 81 cm. Fill the tank with water and pour it into an empty cubic goldfish bowl. It is known that the depth of the goldfish tank is 30 cm from the inside. What is the height of the water in centimeters?
一个圆柱形玻璃水槽，底面直径20厘米，深81厘米，用这个水槽装满水，再倒入一个空的正方体金鱼缸中，已知金鱼缸从里面量的深是30厘米，金鱼缸中的水的高度是多少厘米？
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

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

<gadget id="calculator">30 * 30</gadget>
<output>900</output>

<gadget id="calculator">81 / 900</gadget>
<output>9/100 = around 0.09</output>

<gadget id="calculator">3.14 * 100 * (9/100)</gadget>
<output>28.26</output>

<result>28.26</result>