If a rectangle with an area of 6 square centimeters is enlarged at a ratio of 3:1, what is the area in square centimeters?
把一个面积是6平方厘米的长方形，按3：1的比例放大后，面积是多少平方厘米．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<result>18</result>