Gaosi Factory and Sigao Factory are two adjacent printing factories, printing "Guide" and "Textbook" (a "Guide" and a "Textbook" form a set of teaching materials), each factory's personnel and The equipment can print "Guide" and "Textbook", but due to the different specialties of each factory, Gaosi Factory uses (3/5) time to print "Guide" and (2/5) time to print "Textbook", 900 sets of textbooks are produced every month. Gaosi Factory uses (4/7) time to print "Guide" and (3/7) time to print "Textbook" every month, printing 1200 sets of teaching materials every month. Now the two factories are united to print more textbooks despite their respective strengths, so how many more sets of textbooks are printed every month than in the past?
高思厂和思高厂是两个相邻的印刷厂，印刷《导引》和《课本》(一本《导引》和一本《课本》组成一套教材)，每个厂的人员和设备都能进行《导引》和《课本》的印刷，但是由于各厂的特长不同，高思厂每月用(3/5)的时间印刷《导引》，(2/5)的时间印刷《课本》，每月生产900套教材．高思厂每月用(4/7)的时间印刷《导引》，(3/7)的时间印刷《课本》，每月印刷1200套教材．现在两厂联合起来印刷，尽管发挥各自的特长多印刷教材，那么现在比过去每月多印刷教材多少套？
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">1_200 / (4/7)</gadget>
<output>2_100</output>

<gadget id="calculator">1_200 / (4/7) / 900</gadget>
<output>7/3 = around 2.333333</output>

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

<gadget id="calculator">(7/3) * (2/5)</gadget>
<output>14/15 = around 0.933333</output>

<gadget id="calculator">1 - (14/15)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">900 * (1/15)</gadget>
<output>60</output>

<gadget id="calculator">2_100 + 60</gadget>
<output>2_160</output>

<gadget id="calculator">1_200 + 900</gadget>
<output>2_100</output>

<gadget id="calculator">2_160 - 2_100</gadget>
<output>60</output>

<result>60</result>