The outer radius of a ring is 8 cm and the inner diameter is 8 cm. What is the area of the ring in square centimeters?
一个环形的外圆半径是8厘米，内圆直径是8厘米，这个环形的面积是多少平方厘米．
<gadget id="calculator">8 ** 2</gadget>
<output>64</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

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

<gadget id="calculator">64 - 16</gadget>
<output>48</output>

<gadget id="calculator">3.14 * 48</gadget>
<output>150.72</output>

<result>150.72</result>