A two-layer hollow square has 16 people on the outer layer. How many people are there in this square?
一个两层空心方阵，外层有16人，这个方阵共有多少人．
<gadget id="calculator">16 + 4</gadget>
<output>20</output>

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">3 * 2 * 4</gadget>
<output>24</output>

<result>24</result>