3. (8 points) Fill in each box with a digit so that the multiplication problem is correct. Then, the product of this equation is $\qquad$ .



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【Solution】Solution: According to the problem, we know:
Based on the last digit of the result being 7, we deduce that the unit digit of the first multiplier is 7. Then, based on the first digit of the product being 2, we can deduce that the first multiplier is 27;

Next, considering that 27 multiplied by a number ending in 1 and is a two-digit number, it can only be $27 \times 3=81$;
Therefore, $27 \times 31=837$.
So the answer is: 837