12. (10 points) Cars A and B start from point A at the same time and head towards point B. When car A reaches point B, car B is still 15 kilometers away from point B. If from the midpoint of A and B, the speeds of both cars A and B are doubled, how far from point B will car B be when car A reaches point B?
【Analysis】This problem belongs to the category of travel problems. When the speeds of both car A and car B are doubled, the speed ratio between the two cars remains unchanged, meaning the speed ratio for the entire journey does not change. Solve based on this.

【Solution】Solution: When the speeds of both car A and car B are doubled, the speed ratio between the two cars remains unchanged, meaning the speed ratio for the entire journey does not change. Therefore, when car A reaches point B, car B is still 15 kilometers away from point B. Answer: When car A reaches point B, car B is 15 kilometers away from point B.