A ring has an inner radius of 4 cm and an outer radius of 10 cm, what is the area of the ring?
一个圆环，内圆半径是4厘米，外圆半径是10厘米，圆环的面积是多少．
<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">100 - 16</gadget>
<output>84</output>

<gadget id="calculator">3.14 * 84</gadget>
<output>263.76</output>

<result>263.76</result>