$\"\"$

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The expression is $\"\"$ .

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$\"\"$ (Replace a with $\"\"$ and c with 4.2)

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$\"\"$ (Multiply: $\"\"$ )

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$\"\"$ (Subtract: $\"\"$ )

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$\"\"$ (Absolute value of $\"\"$ )

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$\"\"$ (Multiply: $\"\"$ ) $\"\"$

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The value of the expression is 49.2.