There are two bookshelves on the upper and lower floors. If you take 5 books from the upper layer and put them in the lower layer, then the books on the lower layer are exactly (1/2) of the upper layer. It is known that there were originally 45 books in the lower layer, and how many books were there in the upper layer.
上下两层书架，如果从上层取出5本放入下层，这时下层的书正好是上层的(1/2)．已知下层原来有书45本，上层原来有多少本书．
<gadget id="calculator">45 + 5</gadget>
<output>50</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">50 / (1/2)</gadget>
<output>100</output>

<gadget id="calculator">100 - 45</gadget>
<output>55</output>

<result>55</result>