
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 carbon dioxide emissions in a certain region reach a peak of a billion tons (a > 0) and then begin to decline. The relationship between the carbon dioxide emissions S (in billion tons) and time t (in years) satisfies the function S = a · b^t. If after 7 years, the carbon dioxide emissions are (4a)/5 billion tons, determine the time it takes to achieve carbon neutrality, where the region offsets its own carbon dioxide emissions by (a)/4 billion tons.

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