This is a plane parallel to plane P that is 1 cm above or below it.
Work Step by Step
While this plane is fairly hard to draw, it is not too difficult to describe. Recall, a locus to the plane is the same distance away from the plane at all points. Since the book specifies this distance to be 1 cm, it follows that the answer is a plane parallel to the original plane that is 1 cm above or below it.