Explanation:
that is a strange way to express to situation.
what they mean here is that the perimeters are of identical lengths.
other than the total length the perimeters have nothing in common. therefore, I would have never used the word "congruent" for that. if that would have been the answer to a question like "what statement describes the relationship between the 2 perimeters ?", I would have flagged this as wrong.
anyway, so, the perimeters are of equal length. that means
x + 6 + x + 3 + x + 9 = 2(x + 4) + 2(x + 1)
3x + 18 = 2x + 8 + 2x + 2 = 4x + 10
3x + 8 = 4x
8 = x