11. (12 points) The library purchased 300 books of 5 types: "Zhuangzi", "Confucius", "Mencius", "Laozi", and "Sunzi" for 4500 yuan. Their unit prices (the price of one book) are 10 yuan, 20 yuan, 15 yuan, 28 yuan, and 12 yuan, respectively. The number of "Zhuangzi" and "Confucius" books is the same, and the number of "Sunzi" books is 15 more than 4 times the number of "Laozi" books. In this batch of books, the number of "Sunzi" books is $\qquad$.

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11. (12 points) The library purchased 300 books of 5 types: "Zhuangzi", "Confucius", "Mencius", "Laozi", and "Sunzi" for 4500 yuan. Their unit prices (the price of one book) are 10 yuan, 20 yuan, 15 yuan, 28 yuan, and 12 yuan, respectively. The number of "Zhuangzi" and "Confucius" books is the same, and the number of "Sunzi" books is 15 more than 4 times the number of "Laozi" books. In this batch of books, the number of "Sunzi" books is 195 _books.
【Solution】Solution: The average price per book is:
$$
4500 \div 300=15 \text { (yuan) }
$$

Since the number of "Zhuangzi" and "Confucius" books is the same, $(10+20) \div 2=15$ (yuan),
we can consider the price of "Zhuangzi" and "Confucius" books to be 15 yuan each, and the price of "Mencius" is already 15 yuan, so we only need the average price of "Laozi" and "Sunzi" books to be 15 yuan;
$$
\begin{array}{l}
\{15 \times(15-12) \div[(28-15)-(15-12) \times 4]\} \times 4+15 \\
=[45 \div(13-12)] \times 4+15 \\
=45 \times 4+15 \\
=180+15 \\
=195 \text { (books) }
\end{array}
$$

Answer: In this batch of books, the number of "Sunzi" books is 195.
Therefore, the answer is: 195.