If the outer radius of a ring is 10cm and the inner radius is 8cm, what is its area?
一个圆环的外圆半径是10cm，内圆半径是8cm，那么它的面积是多少．
<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>