Xiaopang borrowed an interesting book. At the beginning, he read 25 pages a day, so he could finish it in 15 days. After reading it for 3 days, Xiaopang doubled the number of pages he read every day. How many days?
小胖借了一本有趣的书，刚开始每天看25页，这样15天能看完，实际看了3天后，小胖每天看书的页数增加到2倍，那么看完这本书还需要几天？
<gadget id="calculator">25 * 15</gadget>
<output>375</output>

<gadget id="calculator">25 * 3</gadget>
<output>75</output>

<gadget id="calculator">375 - 75</gadget>
<output>300</output>

<gadget id="calculator">25 * 2</gadget>
<output>50</output>

<gadget id="calculator">300 / 50</gadget>
<output>6</output>

<result>6</result>