
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
For a given arithmetic series, the sum of the first $100$ terms is $800$, and the sum of the next $100$ terms is $7500$. Find the first term of the series.
A) -25.85
B) -24.835
C) -21.5
D) -20.5
E) -15.335

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