In order to exercise his body, Uncle Zhao walked for 3 hours every day. He first walked on the flat road, then went up the mountain, and finally returned to the same road. Suppose Uncle Zhao walks 4 kilometers per hour on a flat road, 3 kilometers per hour uphill, and 6 kilometers per hour downhill. How many kilometers does he walk in total during his daily exercise?
赵伯伯为锻炼身体，每天步行3小时，他先走平路，然后上山，最后又原路返回．假设赵伯伯在平路上每小时行4千米，上山每小时行3千米，下山每小时行6千米，在每天锻炼中，他共行多少千米？
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<result>12</result>