There are two bookshelves on the upper and lower floors. If 15 books are taken from the upper layer and placed in the lower layer, then the books on the lower layer are exactly the ones on the upper layer (5/7). It is known that there were originally 35 books in the lower level, and how many books were there in the upper level?
上下两层书架，如果从上层取出15本放入下层，这时下层的书正好是上层的(5/7)．已知下层原来有书35本，上层原来有书多少本？
<gadget id="calculator">15 + 35</gadget>
<output>50</output>

<gadget id="calculator">7 + 5</gadget>
<output>12</output>

<gadget id="calculator">5 / 12</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">50 / (5/12)</gadget>
<output>120</output>

<gadget id="calculator">120 - 35</gadget>
<output>85</output>

<result>85</result>