The total area of the garden in the middle of the street is 30,000 m**2, of which buildings and roads account for 30% of the total area of the park, and the rest is green space. How many square meters is the green area of the garden in the middle of the street?
街心花园的总面积为30000米**2，其中建筑、道路等占公园总面积的30%，其余为绿地，街心花园的绿地面积有多少平方米．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">30_000 * (7/10)</gadget>
<output>21_000</output>

<result>21_000</result>