An annular washer, the diameter of the inner circle is 6cm, and the diameter of the outer circle is 10cm, what is the area of the washer in cm**2.
一个环形垫圈，内圆直径是6cm，外圆直径是10cm，这个垫圈的面积是多少cm**2．
<gadget id="calculator">10 / 2</gadget>
<output>5</output>

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

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">25 - 9</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<result>50.24</result>