Fangfang has been reading a famous book for 12 days, with a total of 300 pages. At this speed, I can watch all of them in another 16 days. How many pages are left unread?
芳芳看一本名著，已经看了12天，共看了300页．照这样的速度，再看16天就能全部看完．还剩多少页没有看？
<gadget id="calculator">300 / 12</gadget>
<output>25</output>

<gadget id="calculator">25 * 16</gadget>
<output>400</output>

<result>400</result>