A circular iron sheet has an outer radius of 40 cm and a ring width of 10 cm. What is the area of the ring iron sheet in square centimeters?
一个环形铁皮的外半径是40厘米，环宽10厘米．环形铁皮的面积多少平方厘米？
<gadget id="calculator">40 ** 2</gadget>
<output>1_600</output>

<gadget id="calculator">40 - 10</gadget>
<output>30</output>

<gadget id="calculator">30 ** 2</gadget>
<output>900</output>

<gadget id="calculator">1_600 - 900</gadget>
<output>700</output>

<gadget id="calculator">3.14 * 700</gadget>
<output>2_198</output>

<result>2_198</result>