
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
What is the sum of all real numbers $x$ for which the median of the numbers $3, 7, 9, 15,$ and $x$ is equal to the mean of those five numbers?
A) 19.5  
B) 20.5  
C) 21.5  
D) 22.5  
E) 23.5

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