The area of a circle is 12.56 square centimeters. If the radius increases by 1 centimeter, how much square centimeters does the area increase?
一个圆的面积是12.56平方厘米，如果半径增加1厘米，则面积增加多少平方厘米．
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

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

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<gadget id="calculator">28.26 - 12.56</gadget>
<output>15.7</output>

<result>15.7</result>