The silver part of the disc is a ring, the radius of the inner circle is 2cm, and the radius of the outer circle is 7cm. What is the area of the circle in square centimeters?
光盘的银色部分是一个圆环，内圆半径是2cm，外圆半径是7cm，圆环面积是多少平方厘米．
<gadget id="calculator">7 ** 2</gadget>
<output>49</output>

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

<gadget id="calculator">49 - 4</gadget>
<output>45</output>

<gadget id="calculator">3.14 * 45</gadget>
<output>141.3</output>

<result>141.3</result>