
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 quadrilateral $ABCD$, side lengths $AB,~ BC,~$ and $CD$ are $5$, $7$, and $15$, respectively. If $\sin B = -\cos C = \frac{7}{25}$ and both $\angle B$ and $\angle C$ are obtuse, determine the length of side $AD$.
A) $13$
B) $4\sqrt{13}$
C) $14$
D) $18$
E) $16$

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