A ring-shaped piece of iron has an inner diameter of 14 cm and an outer diameter of 18 cm. What is the area of the ring-shaped piece of iron?
一个环形铁片，内圆直径是14厘米，外圆直径是18厘米，这个环形铁片的面积是多少？
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">9 ** 2</gadget>
<output>81</output>

<gadget id="calculator">14 / 2</gadget>
<output>7</output>

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

<gadget id="calculator">81 - 49</gadget>
<output>32</output>

<gadget id="calculator">3.14 * 32</gadget>
<output>100.48</output>

<result>100.48</result>