One day, Xiaoqiang set off from home on foot at 8 am. He walked on a flat road first, then climbed to the top of the mountain, then returned along the same road, and returned home at 11 am that day. It is known that he walks 4 kilometers per hour on the flat road, 3 kilometers per hour on the uphill, and 6 kilometers per hour on the downhill, how many kilometers did Xiaoqiang travel this time?
某天，小强于上午8点从家里步行出发，他先走一段平路，再爬山到达山顶，然后沿原路返回，于当天上午11点回到家中．已知他在平路上每小时走4千米，上山每小时走3千米，下山每小时走6千米，则小强这一次旅行共走了多少千米的路程．
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<result>12</result>