Sarah and James are training for a marathon. Sarah runs at a constant speed of 8 miles per hour, while James runs at a constant speed of 6 miles per hour. They both start running at the same time but from different starting points. After running for 1.5 hours, Sarah is 3 miles ahead of James. How far apart were they when they started? Let's think step by step and output the final answer within \boxed{}.
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