A person travels from place A to place B. He first walks a section of flat road, then goes uphill to reach place B, and then returns to place A along the original road. It takes 2 hours. It is known that the flat road travels 4 kilometers per hour, and the uphill travel is 3 kilometers per hour. Kilometers, downhill at 6 kilometers per hour, how many kilometers has he traveled in total?
某人从甲地到乙地，先走一段平路后经上坡到达乙地，再沿原路返回甲地共用2小时，已知平路每小时行4千米，上坡每小时行3千米，下坡每小时行6千米，他一共行了多少千米？
<result>4</result>