A group of students stands in a square matrix of 20 rows and 20 columns. If 4 rows and 4 columns are removed, how many people will be reduced?
一队学生站成20行20列方阵，如果去掉4行4列，那么要减少多少人？
<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">16 * 16</gadget>
<output>256</output>

<gadget id="calculator">400 - 256</gadget>
<output>144</output>

<result>144</result>