If the radius of the circle is increased from 3 cm to 4 cm, the area of the circle increases by how many square centimeters.
圆的半径由3厘米增加到4厘米，圆的面积增加了多少平方厘米．
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">16 - 9</gadget>
<output>7</output>

<gadget id="calculator">3.14 * 7</gadget>
<output>21.98</output>

<result>21.98</result>