
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 triangle $\triangle ABC$, the sides opposite to angles A, B, and C are of lengths $a$, $b$, and $c$ respectively. Given the vectors $\overrightarrow {m} = (a+b, \sin C)$ and $\overrightarrow {n} = (\sqrt {3} a+c, \sin B-\sin A)$. If $\overrightarrow {m}$ is parallel to $\overrightarrow {n}$, find the magnitude of angle B.

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