土地是重要的生产资料，尤其是在生产力还不发达的古代社会，统治者更是十分重视土地问题的解决。商鞅变法、北魏孝文帝改革、俄国农奴制改革是如何解决土地问题的？这一问题的解决分别产生了什么影响？

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货车速度与客车速度的比是3：4，两车同时从甲、乙两站相对行驶，在离中点6千米处相遇。甲、 乙两地相距多少千米？