There is a ring with an inner diameter of 10 cm and an outer diameter of 20 cm, what is the area of the ring in square centimetres?
有一个圆环，内直径是10厘米，外直径是20厘米，圆环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>