Wang Fang read a 320-page story book, and read 120 pages in the first 15 days. According to this calculation, how many days are left to finish reading?
王芳看一本320页的故事书，前15天看了120页，照这样计算，剩下的几天看完？
<gadget id="calculator">120 / 15</gadget>
<output>8</output>

<gadget id="calculator">320 / 8</gadget>
<output>40</output>

<gadget id="calculator">40 - 15</gadget>
<output>25</output>

<result>25</result>