A circular fountain with a diameter of 20m is planted with a 4m wide circular lawn around it, how many square meters of lawn should be planted?
一个直径20m的圆形喷水池，在它的周围种植4m宽的环形草坪，需种植草坪多少平方米？
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 + 4</gadget>
<output>14</output>

<gadget id="calculator">14 ** 2</gadget>
<output>196</output>

<gadget id="calculator">3.14 * 196</gadget>
<output>615.44</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<gadget id="calculator">615.44 - 314</gadget>
<output>301.44</output>

<result>301.44</result>