Melt two cubes of iron with a side length of 2 decimeters into a large cuboid. The height of this large cuboid is 4 decimeters, and the bottom is a square. What is the side length of the bottom?
把两块棱长是2分米的正方体铁块熔成一个大长方体，这个大长方体的高是4分米，底面是一个正方形，底面边长是多少？
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