A ring has an inner radius of 6 cm and an outer radius of 8 cm, what is its area in square centimetres?
一个圆环，内圆半径是6厘米，外圆半径是8厘米，它的面积是多少平方厘米．
<gadget id="calculator">8 ** 2</gadget>
<output>64</output>

<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

<gadget id="calculator">64 - 36</gadget>
<output>28</output>

<gadget id="calculator">3.14 * 28</gadget>
<output>87.92</output>

<result>87.92</result>