The ratio of the number of people who subscribed to "Juvenile Science" in Class Six 1 and Class Six 2 is 3:4. There are 21 people in Class Six 1. How many people are there in the two classes?
六1班和六2班订《少年科学》的人数比是3：4，六1班有21人订，两个班一共有多少人？
<gadget id="calculator">3 + 4</gadget>
<output>7</output>

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

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

<result>49</result>