
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
When mailing a letter at the post office, the postage is 0.8 yuan for a letter weighing no more than 20g, 1.6 yuan for a letter weighing more than 20g but not exceeding 40g, and so on, with an additional 0.8 yuan for every additional 20g (for letters weighing within 100g). If someone sends a letter weighing 78.5g, how much postage should they pay?

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