3. (10 points) A store bought a batch of greeting cards at 21 cents each, and sold them for a total of 14.57 yuan. If each card was sold at the same price, and the selling price did not exceed twice the purchase price, then the store made a profit of $\qquad$ cents.

保留源文本的换行和格式，直接输出翻译结果如下：

3. (10 points) A store bought a batch of greeting cards at 21 cents each, and sold them for a total of 14.57 yuan. If each card was sold at the same price, and the selling price did not exceed twice the purchase price, then the store made a profit of $\qquad$ cents.
【Analysis】Converting 14.57 yuan to an integer is 1457 fen, the selling price should be an odd number not exceeding 42, and it is easy to try out the answer.
【Solution】1457 decomposed into prime factors is $1457=31 \times 47, 47$ exceeds twice 21, 31 meets the condition, so the selling price is 31 fen, and the quantity is 47 pieces, $47 \times(31-21)=470$ fen $=47$ jiao. Therefore, the answer is: 47.