There are three groups of students playing games, each group has 12 people. There were as many boys in the first group as there were girls in the second group. The third group has 4 girls. How many boys are there in these three groups of students?
有三组同学做游戏，每组有12人．第一组的男生与第二组中的女生人数同样多．第三组有4名是女生．这三组学生中一共有男生多少人？
<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<gadget id="calculator">12 + 8</gadget>
<output>20</output>

<result>20</result>