In a plywood with a length of 42 decimeters and a width of 20 decimeters, take the largest square plywood, what is the area of the removed square plywood?
在一个长为42分米，宽为20分米的胶合板中，取一块最大的正方形胶合板，取下的正方形胶合板的面积是多少平方分米．
<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<result>400</result>