There are 210 books in the school library. Among them, new books accounted for (5/7), and after buying some new books, the number of new books accounted for (4/5) of the existing books. How many new books are there in the library now?
校图书室有图书210本．其中新书占(5/7)，又买进一些新书后，新书本数占现有图书的(4/5)．现在图书室一共有多少本新书？
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">1 - (5/7)</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(2/7) / (1/5)</gadget>
<output>10/7 = around 1.428571</output>

<gadget id="calculator">210 * (10/7)</gadget>
<output>300</output>

<result>300</result>