In a cuboid container with a length of 20 decimeters and a width of 15 decimeters, there is water 20 decimeters deep. Now sink a cube iron block with a side length of 15 decimeters in the water, how many decimeters is the water depth in the container at this time?
在一个长20分米，宽15分米的长方体容器中，有20分米深的水．现在在水中沉入一个棱长15分米的正方体铁块，这时容器中的水深多少分米？
<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<gadget id="calculator">15 / 300</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">15 * 15 * (1/20)</gadget>
<output>45/4 = around 11.25</output>

<gadget id="calculator">(45/4) + 20</gadget>
<output>125/4 = around 31.25</output>

<result>125/4 = around 31.25</result>