Zhang Xing borrowed a novel from the library. If he reads 30 pages a day, he can finish it in 18 days; however, the maximum borrowing period stipulated by the library is 12 days, and he must finish the novel within the stipulated time. , how many pages does he read on average every day? (solution by equation)
张星从图书馆借了一本小说书，如果每天看30页，18天可以看完；但图书馆规定的最长借阅期限是12天，要在规定的时间内把这本小说书看完，他平均每天要多看多少页？(用方程解)
<gadget id="calculator">18 * 30</gadget>
<output>540</output>

<gadget id="calculator">540 / 12</gadget>
<output>45</output>

<gadget id="calculator">45 - 30</gadget>
<output>15</output>

<result>15</result>