The radius of a circle is 2 meters. If the radius of this circle is increased by 1 meter, how much square meters will its area increase?
一个圆的半径是2米，如果把这个圆的半径增加1米，那么它的面积增加多少平方米？
<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">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

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

<result>15.7</result>