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The term "prism", by default, means "the right prism", if otherwise is not specified.
So, the term "prism" in this context means "the right prism".
The term "truncated prism" describes the prism cut by a plane, by the definition.
But then the condition describes an IMPOSSIBLE situation for a rectangular prism with a square base.
The situation under this condition may happen only if the base of a right prism is a quadrilateral different from a rectangle.
After this discussion I conclude that the problem's condition and its question are not adequate.
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When the problem comes to the forum with incorrect condition, it is not my (as the tutor) duty to explain why the condition is wrong/false.
In opposite, it is your responsibility to provide the correct input.
In this situation, it is not me who should "explain".
In this situation it is you who should explain why do you post inadequate (= wrong) problem to the forum.