Study the following figure, where two concentric circles share center C.
Segment AB is a diameter of the larger circle.
Segment AB intersects a chord of the smaller circle, PQ, at a right angle at point Z.
Segment AB intersects a chord of the larger circle, MN, at a right angle at point 0.
If MO=7x-4, and NO=6x, what is the length of MN
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