Xiaohong reads a book, she reads 16 pages every day, half of the book is read in 5 days. After that, she read 4 more pages every day than before. How many days did it take to finish reading this book?
小红读一本书，她每天读16页，5天读了全书的一半．此后她每天比原来多读4页，读完这本书一共用了多少天？
<gadget id="calculator">16 + 4</gadget>
<output>20</output>

<gadget id="calculator">5 / 20</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">16 * (1/4)</gadget>
<output>4</output>

<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<result>9</result>