The original number of science books in the school library is 2/5 of the story books, and now 60 science books are purchased. At this time, the ratio of science books to story books is 4:7. How many story books were there in the library?
学校图书室原有科技书的本数是故事书的(2/5)，现在又购进60本科技书，这时科技书与故事书的比是4：7．图书室原来有多少本故事书？
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(4/7) - (2/5)</gadget>
<output>6/35 = around 0.171429</output>

<gadget id="calculator">60 / (6/35)</gadget>
<output>350</output>

<result>350</result>