13. (10 points) Xiaoqiao spent 660 yuan to buy several 4-yuan and 8-yuan World Expo stamps. If the number of 8-yuan stamps is 30 more than the number of 4-yuan stamps, then Xiaoqiao bought $\qquad$ stamps in total.
【Solution】Solution: Let the number of 4 yuan stamps be $x$, then the number of 8 yuan stamps is $x+30$,
$$
\begin{array}{l}
4 x+8(x+30)=660 \\
x=35 \\
35+30=65 \text { (pieces) } \\
35+65=100 \text { (pieces) }
\end{array}
$$

Answer: Xiaoqiao bought a total of 100 stamps.
Therefore, the answer is: 100.