The radius of the inner circle of a ring is 2 decimeters, and the width of the ring is 1 decimeter. Find the area of the ring.
一个环形内圆半径2分米，环宽1分米，求环形面积．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

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

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">28.26 - 12.56</gadget>
<output>15.7</output>

<result>15.7</result>