Cut a largest square out of a rectangle whose length is 10 decimeters and width is 7 decimeters. What is the perimeter of this square?
在一个长是10分米，宽是7分米的长方形中剪一个最大的正方形，这个正方形的周长是多少分米．
<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<result>28</result>