There are two classes, A and B. The number of boys in class A is 4/5 of the number of boys in class B, and the number of girls in class A is 1/3 of the number of girls in class B. The difference between the number of boys and girls in class A and B is 21 people (both classes have 21 more boys than girls). How many people are there in Class A and Class B?
有甲乙两个班，甲班男生人数是乙班男生人数的(4/5)，甲班女生人数是乙班女生人数的(1/3)，甲乙两班各自的男女人数之差都是21人(两班都是男生比女生多21人)．求甲乙两班共有多少人？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(4/5) * 21</gadget>
<output>84/5 = around 16.8</output>

<gadget id="calculator">21 - (84/5)</gadget>
<output>21/5 = around 4.2</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(4/5) - (1/3)</gadget>
<output>7/15 = around 0.466667</output>

<gadget id="calculator">(21/5) / (7/15)</gadget>
<output>9</output>

<gadget id="calculator">9 + 21</gadget>
<output>30</output>

<gadget id="calculator">30 * (4/5)</gadget>
<output>24</output>

<gadget id="calculator">24 - 21</gadget>
<output>3</output>

<gadget id="calculator">9 + 30 + 24 + 3</gadget>
<output>66</output>

<result>66</result>