12. There are two buckets, a large one and a small one, both containing some water. It is known that the weight of the water in the large bucket is half that in the small bucket. If 30 kilograms of water are added to the large bucket, the weight of the water in the large bucket becomes three times that in the small bucket. Originally, the large bucket contained $\qquad$ water.
【Answer】6
【Analysis】According to the line segment diagram, it is found that 30 kilograms corresponds to (6-1) = 5 parts. So the original amount of water in the large bucket = 30 ÷ (6-1) = 6 kilograms.