There are two rectangular parallelepiped glass fish tanks without a cover, the first fish tank has water in it and the second fish tank has no water in it. Measured from the inside, the length of the first fish tank is 5dm, the width is 4dm, and the height of the water surface is 3dm; the length of the second fish tank is 5dm, the width is 2dm, and the depth is 5dm. Pour part of the water in the first fish tank into the second fish tank so that the height of the water surface in the two fish tanks is the same. How many centimeters is the water surface now?
有两个无盖的长方体玻璃鱼缸，第一个鱼缸里有水，第二个鱼缸里没水．从里面量，第一个鱼缸长5dm，宽4dm，水面高3dm；第二个鱼缸长5dm，宽2dm，深5dm．将第一个鱼缸中的一部分水倒入第二个鱼缸，使两个鱼缸里水面的高度一样，现在水面高多少厘米？
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<gadget id="calculator">3 / 30</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">5 * 4 * (1/10) * 10</gadget>
<output>20</output>

<result>20</result>