0
6. 【Solution】Since the first digit of the difference is 8, the first digit of the minuend is 9, and the first digit of the subtrahend is 1. On the second digit, the difference between the two numbers is 9, so the second digit of the minuend is 9, and the second digit of the subtrahend is 0. Therefore, the product of the six digits in the boxes is 0.

Answer: The product of the six digits in the boxes is 0.
6. As shown in the figure below, it is a subtraction problem of two three-digit numbers, where each box represents a digit. Question: What is the product of the six digits in these boxes?



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