A ring has an inner diameter of 10 cm and a ring width of 2 cm. What is the area of the ring?
一个环形，内直径是10厘米，环宽是2厘米，这个圆环的面积是多少．
<gadget id="calculator">10 + 2 + 2</gadget>
<output>14</output>

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

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

<gadget id="calculator">3.14 * 49</gadget>
<output>153.86</output>

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

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

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<gadget id="calculator">153.86 - 78.5</gadget>
<output>75.36</output>

<result>75.36</result>