A ring has an inner radius of 2 cm and an outer diameter of 5 cm. What is the area of the circle in square centimetres.
一环形内半径为2厘米，外直径为5厘米．环形面积是多少平方厘米．
<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">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">(25/4) - 4</gadget>
<output>9/4 = around 2.25</output>

<gadget id="calculator">3.14 * (9/4)</gadget>
<output>7.065</output>

<result>7.065</result>