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As stated in the statement of the question, EF is a bisector of CD, so point G is the median point of CD, so CG = GD
5X - 1 = 7X - 13
X = 6
EF = EG + GF
6X - 4 = EG + 13 x = 6, so
6·6 - 4 = EG + 13
(see attachment)
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