ring part has an outer radius of 20 cm and an inner radius of 16 cm. What is the area of the circle in square centimeters?
一个圆环零件，外圆半径是20厘米，内圆半径是16厘米．环形的面积是多少平方厘米？
<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">16 ** 2</gadget>
<output>256</output>

<gadget id="calculator">400 - 256</gadget>
<output>144</output>

<gadget id="calculator">3.14 * 144</gadget>
<output>452.16</output>

<result>452.16</result>