
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
To investigate the PM2.5 value in cities, 36 cities are divided into three groups: Group A, Group B, and Group C, with corresponding numbers of cities being 6, 12, and 18 respectively. If stratified sampling is used to select 12 cities, then the number of cities to be sampled from Group B is __________.

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