Cup A contains 40 kg of salt water containing 20% salt, and cup B contains 60 kg of salt water containing 4% salt. Now take some salt water from cup A and put it into cup C, and then take some salt water from cup B Into a small cup. Then pour the D cup of salt water into the A cup, and pour the C cup of salt water into the B cup. As a result, the A and B cups become two cups of salt water with the same salt concentration. If it is known that the weight of the brine taken out of cup B and poured into cup D is 6 times the weight of the brine taken out of cup A and poured into cup C, try to determine how many kilograms of brine was taken out of cup A and poured into cup C?
甲杯中装有含盐20%的盐水40千克，乙杯中装有含盐4%的盐水60千克，现从甲杯中取出一些盐水放入丙杯，再从乙杯中取一些盐水放入丁杯．然后将丁杯盐水全倒入甲杯，把丙杯盐水全倒入乙杯，结果甲、乙两杯成为含盐浓度相同的两杯盐水．若已知从乙杯取出并倒入丁杯的盐水重量是从甲杯取出并倒入丙杯盐水重量的6倍，试确定从甲杯取出并倒入丙杯的盐水多少千克？
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