Purchase a batch of story books and science books from the school library. The ratio of the number of story books purchased to the number of science books is 7:5. At the request of students, the school decided to purchase another 390 story books. At this time, the total number of stories purchased The ratio to the number of science and technology books is 4:1. How many science and technology books are purchased by the school?
购进学校图书馆一批故事书与科技书，购进故事书本数与科技书本数的比是7：5，应学生的要求，学校决定再购进390本故事书，这时购进故事总数与科技书本数的比是4：1，学校购进科技书多少本．
<gadget id="calculator">4 / 1</gadget>
<output>4</output>

<gadget id="calculator">7 / 5</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">4 - (7/5)</gadget>
<output>13/5 = around 2.6</output>

<gadget id="calculator">390 / (13/5)</gadget>
<output>150</output>

<result>150</result>