**AMC 10 Mock Exam Question 7**

The $8\times18$ rectangle $ABCD$ is cut into two congruent hexagons, as shown, in such a way that the two hexagons can be repositioned without overlap to form a square.

What is $y$?

$\mathbf{(A) } 6\qquad\mathbf{(B) } 7\qquad\mathbf{(C) } 8\qquad\mathbf{(D) } 9\qquad\mathbf{(E) } 10$

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