rectangular parallelepiped iron sheet with a width of 16 decimeters, cut off a square with a side length of 4 decimeters from its four corners, and then weld it into a rectangular parallelepiped box without a cover. If the volume of this box is 786 cubic decimeters , so how many square decimeters is the original area of this iron sheet?
一块宽是16分米的长方体铁皮，它的四个角上分别剪去边长是4分米的正方形，然后把它焊接成一个无盖的长方体箱子，如果这个箱子的容积是786立方分米，那么这块铁皮原来的面积是多少平方分米？
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">16 - 8</gadget>
<output>8</output>

<gadget id="calculator">4 * 8</gadget>
<output>32</output>

<gadget id="calculator">786 / 32</gadget>
<output>393/16 = around 24.5625</output>

<gadget id="calculator">(393/16) + 8</gadget>
<output>521/16 = around 32.5625</output>

<gadget id="calculator">(521/16) * 16</gadget>
<output>521</output>

<result>521</result>