$\"\"$

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The equation is $\"\"$ .

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Divide each side by 400.

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$\"\"$

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$\"\"$

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$\"\"$

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Apply formula: If $\"\"$ , then $\"\"$ .

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$\"\"$

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$\"\"$

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Apply change base formula: $\"\"$ .

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$\"\"$

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Using calculator: $\"\"$ .

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$\"\"$

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(Divide: $\"\"$ )

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$\"\"$

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$\"\"$

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The solution is approximately $\"\"$ .