The area of a circle is 4 square centimeters. If its radius is enlarged by a ratio of 2:1, what is the area of the circle after enlargement?
一个圆的面积是4平方厘米，把它的半径按2：1的比例放大，放大后圆的面积是多少平方厘米．
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<result>16</result>