6. (5 points) Using the digits $2$, $0$, $1$, and $5$, we can form $\qquad$ unique three-digit numbers where the digits do not repeat, and these three-digit numbers are multiples of 5.
【Solution】Solution: $3 \times 2 \times 1+2 \times 2 \times 1$
$$
\begin{array}{l}
=6+4 \\
=10 \text { (numbers) }
\end{array}
$$

Answer: Using the four digits 2, 0, 1, and 5, 10 different three-digit numbers can be formed without repeating digits, such that these three-digit numbers are multiples of 5.

Therefore, the answer is: 10.

