If the area of a circle is 10 square centimeters, if its radius is doubled, what is the area of the circle in square centimeters?
一个圆的面积是10平方厘米，如果把它的半径扩大到原来的2倍，那么这个圆的面积变为多少平方厘米．
<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<result>40</result>