
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
The younger sister is 18 years old this year, and the elder sister is 26 years old this year. When the sum of their ages was 20 years, the elder sister was $\qquad$ years old.

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