The roller of a road roller is 4 meters long and 1 meter in diameter. If it rolls 20 times, how many square meters will it cover?
一台压路机的滚轮长4米，直径是1米，如果它滚动20圈，压过的面积是多少平方米？
<gadget id="calculator">3.14 * 1 * 20 * 4</gadget>
<output>251.2</output>

<result>251.2</result>