On the four corners of a rectangular cardboard with a length of 20 cm, cut off a square with a side length of 2 cm, and then fold it into a rectangular parallelepiped carton without a cover. The volume of this carton is 256 cubic centimeters. What is the area in square centimeters of the original rectangular cardboard used to make this carton?
在一块长20厘米的长方形的硬纸板的四个角上，分别剪去边长是2厘米的正方形后，然后折成一个无盖的长方体的纸盒，这个纸盒的体积是256立方厘米，求做成这个纸盒的原长方形硬纸板的面积是多少平方厘米？
<gadget id="calculator">256 / 2</gadget>
<output>128</output>

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

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

<gadget id="calculator">128 / 16</gadget>
<output>8</output>

<gadget id="calculator">8 + 4</gadget>
<output>12</output>

<gadget id="calculator">20 * 12</gadget>
<output>240</output>

<result>240</result>