Cut a cuboid with a square base into two equal cubes. The surface area of the cuboid is 40 square decimeters. How many decimeters is the side length of each cube?
把一个底面是正方形的长方体裁成相等的两个正方体，长方体的表面积是40平方分米，每个正方体的棱长是多少分米？
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