A library has 20 identical bookshelves, each shelf has 4 layers, and each layer holds 240 books. How many books can these bookshelves hold in total?
一个图书馆有20个同样的书架，每个书架有4层，每层放240本书．这些书架一共能放多少本书？
<gadget id="calculator">240 * 4 * 20</gadget>
<output>19_200</output>

<result>19_200</result>