?? ???15??????6??????????? ???
????:1???????????:?????????
2???????150??
3???300??????
4???????????
5?????????????
????????????????7?????28?????? (?? ???)?,??28????,????15??6??
28??8???,??,??,?????21??????,??????????????????????????,?????????
?????,??21?,???15??,6???????????,?????????????,???????????(?????????????)
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