The ratio of the number of people who subscribed to "Youth Science" in Class 61 and Class 62 was 3:4, and the two classes ordered 49 copies in total. How many copies are ordered for the second class than the first class?
六一班和六二班订《少年科学》的人数比是3：4，两个班共订了49份．二班比一班多订多少份？
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">49 * (4/7)</gadget>
<output>28</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">49 * (3/7)</gadget>
<output>21</output>

<gadget id="calculator">28 - 21</gadget>
<output>7</output>

<result>7</result>