A circular piece of iron has an outer radius of 15 cm and an inner radius of 8 cm. What is the area of this circular piece of iron in square centimeters?
一块环形铁片，外圆半径15厘米，内圆半径8厘米．这块环形铁片的面积是多少平方厘米？
<gadget id="calculator">15 ** 2</gadget>
<output>225</output>

<gadget id="calculator">8 ** 2</gadget>
<output>64</output>

<gadget id="calculator">225 - 64</gadget>
<output>161</output>

<gadget id="calculator">3.14 * 161</gadget>
<output>505.54</output>

<result>505.54</result>