
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
A class went on a study trip to a revolutionary old district. There are two types of fast food available at the study base, type A and type B. If buying one serving of type A fast food costs $30$ yuan, and buying one serving of type B fast food costs $20$ yuan, then buying $a$ servings of type A fast food and $b$ servings of type B fast food together costs ______ yuan. (Express your answer in terms of $a$ and $b$)

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