
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 $\triangle ABC$, the sides opposite to angles $A$, $B$, and $C$ are denoted as $a$, $b$, and $c$ respectively, and $S$ represents the area of the triangle. It is given that $2\sin B-2\sin ^{2}B-\cos 2B= \sqrt {3}-1$.  
(I) Find the magnitude of angle $B$;  
(II) If $B$ is an acute angle, $a=6$, and $S=6 \sqrt {3}$, find the value of $b$.

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