If the radius of the inner circle is 2 cm and the width of the ring is 1 cm, what is the area of the ring in square centimeters?
一个环形，如果内圆的半径是2厘米，环形的宽度是1厘米，那么环形的面积是多少平方厘米．
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<gadget id="calculator">9 - 4</gadget>
<output>5</output>

<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

<result>15.7</result>