There is a mixture of two drugs P and Q in two bottles of A and B, and the concentration ratio is: P in bottle A: Q=3:5, and P: Q=3:7 in bottle B. Several grams are mixed, so that in the mixture taken out, there are 6 grams of drug P and 12 grams of drug Q. What is the number of grams of the mixture taken out of bottle A?
甲乙两瓶里有两种药物P、Q的混合物，其浓含量比为：甲瓶中P：Q=3：5，乙瓶中P：Q=3：7，现从甲乙两瓶中各取若干克混合，使得在取出的混合剂中，药物P有6克，药物Q有12克，则从甲瓶中取出的混合剂的克数是多少．
<result>8</result>