When Xiao Ming reads a book, he has already read 115 pages, and the remaining pages are 20 pages a day, which takes 15 days to finish. How many pages are there in this book?
小明看一本书，已经看了115页，剩下的每天看20页，15天看完．这本书一共多少页？
<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<gadget id="calculator">300 + 115</gadget>
<output>415</output>

<result>415</result>