Wang Li reads a story book. She plans to read 40 pages a day, and she can finish reading it in 15 days. In reality, she read 150 pages in 3 days. How many days did it take to finish reading the book?
王莉读一本故事书，计划每天读40页，15天可以全部读完，实际3天就读了150页，实际用了多少天读完这本书？
<gadget id="calculator">40 * 15</gadget>
<output>600</output>

<gadget id="calculator">150 / 3</gadget>
<output>50</output>

<gadget id="calculator">600 / 50</gadget>
<output>12</output>

<result>12</result>