A ring has an inner diameter of 5 cm and an outer radius of 3 cm. What is the area of the ring in cm**2.
一个圆环，内圆直径5cm，外圆半径3cm，圆环的面积是多少cm**2．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(5/2) ** 2</gadget>
<output>25/4 = around 6.25</output>

<gadget id="calculator">9 - (25/4)</gadget>
<output>11/4 = around 2.75</output>

<gadget id="calculator">3.14 * (11/4)</gadget>
<output>8.635</output>

<result>8.635</result>