When Dongdong organizes the bookcase, he first takes out as many books from the upper layer as the middle layer and puts them in the middle layer, and then takes out as many books from the middle layer as the lower layer and puts them in the lower layer. At this time, there are 48 books in the three layers. It turns out how many books are there on the upper floor.
冬冬在整理书柜时，先从上层取出与中层同样多的书放到中层，再从中层取出与下层同样多的书放到下层，这时三层所放的书都是48本．原来上层有多少本书．
<gadget id="calculator">48 / 2</gadget>
<output>24</output>

<gadget id="calculator">48 + 24</gadget>
<output>72</output>

<gadget id="calculator">72 / 2</gadget>
<output>36</output>

<gadget id="calculator">36 + 48</gadget>
<output>84</output>

<result>84</result>