A ring has an outer diameter of 20 cm and an inner radius of 8 cm. What is the area of the ring in square centimeters?
一个环形，外圆直径为20厘米，内圆半径为8厘米，这个环形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">8 ** 2</gadget>
<output>64</output>

<gadget id="calculator">100 - 64</gadget>
<output>36</output>

<gadget id="calculator">3.14 * 36</gadget>
<output>113.04</output>

<result>113.04</result>