It costs 30 yuan to buy 1 comic book and 2 science books, and 69 yuan to buy the same 3 comic books and 4 science books. How much is a comic book?
买1本漫画书和2本科技书要用30元，买同样的3本漫画书和4本科技书要用69元，一本漫画书多少元？
<gadget id="calculator">69 - 30</gadget>
<output>39</output>

<gadget id="calculator">39 - 30</gadget>
<output>9</output>

<result>9</result>