An annular washer has an inner diameter of 3 cm and an outer diameter of 10 cm. What is the area of the annular washer in square centimetres?
一个环形垫圈，内圆半径是3厘米，外圆直径是10厘米，这个环形垫圈的面积是多少平方厘米．
<gadget id="calculator">10 / 2</gadget>
<output>5</output>

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