There is a rectangular fish pond with a length of 60 meters and a width of 40 meters. If it is to be expanded into a square fish pond, how many square meters will the area be increased at least?
有一个长60米、宽40米的长方形鱼塘，如果要把它扩建成正方形鱼塘，面积至少增加多少平方米？
<gadget id="calculator">60 - 40</gadget>
<output>20</output>

<gadget id="calculator">60 * 20</gadget>
<output>1_200</output>

<result>1_200</result>