A ring-shaped iron piece has an inner diameter of 10cm and an outer diameter of 14cm. What is the area of the ring-shaped iron piece in cm**2.
一种环形铁片，内直径是10cm，外直径是14cm，这个环形铁片的面积是多少cm**2．
<gadget id="calculator">14 / 2</gadget>
<output>7</output>

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

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">49 - 25</gadget>
<output>24</output>

<gadget id="calculator">3.14 * 24</gadget>
<output>75.36</output>

<result>75.36</result>