If two rectangles with a length of 20 cm and a width of 10 cm are used to form a square, what is the area of the formed square?
用两个长20厘米，宽10厘米的长方形，拼成一个正方形，拼成的正方形的面积是多少平方厘米？
<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<result>400</result>