9. (10 points) From the ten digits $0, 1, 2, 3, 4, 5, 6, 7, 8, 9$, select nine digits to form a two-digit number, a three-digit number, and a four-digit number, such that the sum of these three numbers equals 2010. The digit that was not selected is . $\qquad$
【Analysis】According to the method of casting out nines, the sum of the digits of all addends should differ from the sum of the digits of the obtained total by an integer multiple of 9. Since the sum of the digits of 2010 is 3, and $0+1+2+\cdots+9=45$, 6 should be removed from it.

【Solution】Solution: The sum of the digits of the addends and the sum of the digits of the obtained total should differ by an integer multiple of 9.
Since the sum of the digits of 2010 is: $2+0+1+0=3$,
$$
\begin{array}{l}
0+1+2+\cdots+9 \\
=(0+9) \times 10 \div 2 \\
=45
\end{array}
$$
45 is a multiple of 9, and 3 needs to add 6 to become a multiple of 9, so 6 should be removed from it.
Therefore, the answer is: 6.