The inner diameter of a circular iron plate is 10 cm, and the outer diameter is 20 cm, what is its area in square centimeters?
一个环形铁片的内直径是10厘米，外圆直径是20厘米，它的面积是多少平方厘米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

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

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">100 - 25</gadget>
<output>75</output>

<gadget id="calculator">3.14 * 75</gadget>
<output>235.5</output>

<result>235.5</result>