The inner diameter of a circle is 8 cm and the outer radius is 5 cm. What is the area of the circle in square centimetres?
一个圆环的内直径是8厘米，外半径是5厘米，这个圆环的面积是多少平方厘米．
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

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

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<result>28.26</result>