The outer radius of a ring is 1.75 cm and the inner radius is 0.25 cm. What is the area of the ring?
一个环形的外圆半径是1.75厘米，内圆半径是0.25厘米，环形的面积多少．
<gadget id="calculator">1.75 ** 2</gadget>
<output>3.0625</output>

<gadget id="calculator">0.25 ** 2</gadget>
<output>0.0625</output>

<gadget id="calculator">3.0625 - 0.0625</gadget>
<output>3</output>

<gadget id="calculator">3.14 * 3</gadget>
<output>9.42</output>

<result>9.42</result>