Master Zhang made a cover for a jar. He measured the inner diameter of the altar to be 20 cm and the thickness of the wall to be 2 cm. What is the area of the cover so that the cover can just cover the outer edge of the mouth of the jar? square centimeter.
张师傅为一口坛子制作一个坛盖，他量出坛的内直径为20厘米，坛壁的厚度为2厘米，要使坛盖正好能盖住坛口的外沿，这个坛盖的面积是多少平方厘米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 + 2</gadget>
<output>12</output>

<gadget id="calculator">12 ** 2</gadget>
<output>144</output>

<gadget id="calculator">3.14 * 144</gadget>
<output>452.16</output>

<result>452.16</result>