There are 20 bookshelves in the school library, and each shelf holds 420 books. How many books can be placed in total?
学校图书馆有20个书架，每个书架放420本图书，一共可以放多少本图书？
<gadget id="calculator">420 * 20</gadget>
<output>8_400</output>

<result>8_400</result>