A 4-meter-long cuboid steel, with a square cross-section, is cut into two sections, and the surface area increases by 400 square centimeters compared to the original. Find the volume of this bar.
一根长4米的长方体钢材，横截面是正方形，横截成两段后，表面积比原来增加了400平方厘米．求这根钢材的体积．
<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<gadget id="calculator">4 * 50 * 4 * 100</gadget>
<output>80_000</output>

<result>80_000</result>