There are 2 bookshelves in the third-grade teacher's office, each with 3 floors, and an average of 20 books on each floor. How many books are there in total on the shelf?
三年级教师办公室里有2个书架，每个书架有3层，平均每层有20本书．书架上一共有多少本书？
<gadget id="calculator">20 * 3 * 2</gadget>
<output>120</output>

<result>120</result>