A city builds a green belt of 40 kilometers and 5 meters wide around the urban area. How many hectares does this green belt have?
一座城市在城区的周围建一条40千米，宽5米的绿化带，这条绿化带共有多少公顷．
<gadget id="calculator">5 / 10_000</gadget>
<output>1/2_000 = around 0.0005</output>

<gadget id="calculator">40 * 1_000 * (1/2_000)</gadget>
<output>20</output>

<result>20</result>