6. (10 points) Please fill in the blanks in the following equation with the numbers $0-9$, using each number exactly once, or already filling in “1”, “3”, and “0”. If the equation holds true, then the only four-digit minuend in the equation is.
$\square$ 1 $\square$
$\square$ - $\square$
$\square$
$\square$ $\times$ $\square$
$\square$
$\square$ $=2016$
2196
【Solution】Solution: According to the problem, let the letters be as shown in the figure.

First, if the thousand's place of this four-digit number $A \geqslant 3$, it would be impossible to get 2016 after subtraction. Therefore, $A=2$.
Secondly, the product of the two subsequent numbers is an integer, $\overline{3 \mathrm{DE}} \times \overline{\mathrm{FG}}$ is a multiple of 100. So one of these multipliers must be a multiple of 4 and the other a multiple of 25.
Therefore, one of the numbers must end with 75. If $\overline{\mathrm{FG}}=75$, then the product with $\overline{3 \mathrm{DE}}$ would be greater than 200, making the equation impossible. When $\overline{3 D E}=375$, if $\overline{F G} \geqslant 60$, the equation would similarly not hold. Therefore, $\overline{F G}$ must be a multiple of 4 less than 60. Among the remaining numbers $(4,6,8,9)$, only 48 meets the requirement.
Therefore, $\overline{\mathrm{FG}}=48$.
Thus, this four-digit number is $2016+375 \times 0.48=2196$. The original equation is $2196-375 \times 0.48=2016$.
Therefore, the answer is: 2196.