$\"\"$

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Diagonals of a rectangle are congruent.

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So, $\"\"$ .

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$\"\"$ (Definition of congruent segments)

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$\"\"$ (Substitute $\"\"$ )

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$\"\"$ (Add x to each side)

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$\"\"$ (Add 60 to each side)

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$\"\"$ (Divide each side by 5) $\"\"$

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The value of x is 18.