
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
In the arithmetic sequence ${a_n}$, $S_n$ represents the sum of its first $n$ terms. Given that $a_1 = -9$ and $\frac{S_9}{9} - \frac{S_7}{7} = 2$, find the value of $S_{12}$.

Present the answer in LaTex format: \boxed{Your answer}
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