Let's solve the equation step by step and fill in the missing parts.
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Start with the original equation: \(-3x - 9 = -21\)
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Add 9 to both sides: \(-3x = -21 + 9\)
So, \(-3x = -12\)
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Now, divide both sides by -3: \(x = \frac{-12}{-3}\)
This simplifies to: \(x = 4\)
Thus, the completed solution is:
- After adding 9: \(-3x = -12\)
- Final answer for \(x\): \(x = 4\)