There are two layers of books on the bookshelf. If 15 books are taken from the first layer and placed on the second layer, then the number of books in the second layer is exactly the number of books on the first layer (5/7). It is known that there are 35 original books in the second floor, how many more books are there in the first floor than in the second floor?
书架上有两层书，如果从第一层里取出15本放人第二层，这时第二层里的书的本数正好是第一层的(5/7)．已知第二层里原有书35本，第一层里原有的书比第二层原有的书多多少本？
<gadget id="calculator">35 + 15</gadget>
<output>50</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">50 / (5/7)</gadget>
<output>70</output>

<gadget id="calculator">15 - 35</gadget>
<output>-20</output>

<gadget id="calculator">70 + (-20)</gadget>
<output>50</output>

<result>50</result>