How many hectares does a rectangular playground with a length of 400 meters and a width of 100 meters occupy?
长为400米，宽为100米的长方形操场占地多少公顷．
<gadget id="calculator">400 * 100</gadget>
<output>40_000</output>

<gadget id="calculator">40_000 / 10_000</gadget>
<output>4</output>

<result>4</result>