The diameter of the outer circle of a circle is 6 decimeters and the radius of the inner circle is 1 decimeter. What is the area of the circle in square decimeters?
一个圆环的外圆直径是6分米，内圆半径是1分米，这个圆环的面积是多少平方分米．
<gadget id="calculator">6 / 2</gadget>
<output>3</output>

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

<gadget id="calculator">1 ** 2</gadget>
<output>1</output>

<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">3.14 * 8</gadget>
<output>25.12</output>

<result>25.12</result>