A ring has an outer radius of 10 cm and an inner radius of 8 cm. What is the area of the ring in square centimetres?
一个环形，外圆半径是10厘米，内圆半径是8厘米，这个圆环的面积是多少平方厘米．
<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>