To solve the equation \( 21x + 1,998 = 2,243 \), we can follow these steps:
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Subtract 1,998 from both sides: \[ 21x = 2,243 - 1,998 \] \[ 21x = 245 \]
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Now, divide both sides by 21 to solve for \( x \): \[ x = \frac{245}{21} \] \[ x \approx 11.67 \]
Given the options provided (10, 1, 100, 1,000), the closest estimate for \( x \) is 10.