After borrowing 2904 books from the school library, there are still 17697 books left. How many books are there in the school library? (answer in two ways)
学校图书馆借掉2904本书后，还剩下17697本书，学校图书馆里原来有多少本书？(用两种方法解答)
<gadget id="calculator">17_697 + 2_904</gadget>
<output>20_601</output>

<result>20_601</result>