If there are several students, they are arranged in a square matrix first, and then changed into a rectangular matrix. Therefore, the number of columns is reduced by 12, and the number of rows is increased by 30. What is the total number of students?
有学生若干人，先排成方阵，再改成长方阵，因而列数减少12，而行数增加30，则总人数是多少人．
<gadget id="calculator">12 * 30</gadget>
<output>360</output>

<gadget id="calculator">30 - 12</gadget>
<output>18</output>

<gadget id="calculator">360 / 18</gadget>
<output>20</output>

<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<result>400</result>