
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
The function \( f(x) \) satisfies
\[ f(x + f(x)) = 4f(x) \] for all \( x, \) and \( f(1) = 3. \) Find \( f(21). \)

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