To subtract the two fractions \( \frac{x}{3x + 7} - \frac{x}{9x + 21} \), we first need to find a common denominator.
Notice that \( 9x + 21 \) can be factored as \( 3(3x + 7) \).
The common denominator will be \( 3(3x + 7) \).
Now, let's rewrite both fractions with this denominator:
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The first fraction: \[ \frac{x}{3x + 7} = \frac{x \cdot 3}{(3x + 7) \cdot 3} = \frac{3x}{3(3x + 7)} \]
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The second fraction: \[ \frac{x}{9x + 21} = \frac{x}{3(3x + 7)} \]
Now we can subtract the fractions: \[ \frac{3x}{3(3x + 7)} - \frac{x}{3(3x + 7)} = \frac{3x - x}{3(3x + 7)} = \frac{2x}{3(3x + 7)} \]
Thus, the simplified result is: \[ \frac{2x}{9x + 21} \]
Looking at the provided options, the correct answer is: Start Fraction 2 x over 9 x plus 21 End Fraction.