某市要改善城市交通拥挤问题，决定架设立交桥，雇佣A、B两支工程队，如果由B工程队单独施工，用时比A工程队单独施工多4天；如果两个工程队先合作3天，余下的部分交给B工程队完成，所用时间刚好与A工程队单独施工所用时间相同。则由A工程队施工则需要多少天？（ ）

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