Warren the Welder

The math fairy left a new problem in a comment on the last post. I didn't want anyone to miss it so I'm reposting it. Here it goes:

Warren has 3 sheets of tin 36x36. He wishes to make some boxes by cutting equal corners from all sheets. He folds up the sides to form "open top" boxes. Being frugal, he decides to weld the 12 squares into two cubes. How should he do this to maximize the total volume?

Thanks for the problem....whoever you are?

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