The diameter of the ring-shaped iron piece is 20 decimeters, and the radius of the inner circle is 7 decimeters. What is the area of the ring-shaped iron piece?
环形铁片，外圈直径20分米，内圆半径7分米，环形铁片的面积是多少？
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">7 ** 2</gadget>
<output>49</output>

<gadget id="calculator">100 - 49</gadget>
<output>51</output>

<gadget id="calculator">3.14 * 51</gadget>
<output>160.14</output>

<result>160.14</result>