A bookshelf in the library has two floors. After taking 160 books from the upper floor and putting them in the lower floor, the number of books on the upper floor is 40 less than that on the lower floor.
图书室的一个书架有上下两层，从上层拿160本书放入下层后，上层书比下层少40本，原上层比下层多多少本．
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">160 - 20</gadget>
<output>140</output>

<gadget id="calculator">140 * 2</gadget>
<output>280</output>

<result>280</result>