Xiao Ming reads a book and reads 105 pages in the first 3 days, and Xiao Ming finishes the book in 9 days. How many pages does this book have? (proportional solution)
小明看一本书，前3天看了105页，小明又用9天把这本书看完，这本书共有多少页？(比例解)
<gadget id="calculator">105 / 3</gadget>
<output>35</output>

<gadget id="calculator">35 * 9</gadget>
<output>315</output>

<gadget id="calculator">315 + 105</gadget>
<output>420</output>

<result>420</result>