When Xiao Ming reads a book, he has already read 105 pages, and the remaining pages are 20 pages a day, and he needs 20 days to finish. How many pages are there in this book?
小明看一本书，已经看了105页，剩下的每天看20页，还要看20天看完．这本书一共多少页？
<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<gadget id="calculator">400 + 105</gadget>
<output>505</output>

<result>505</result>