
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
Solve the equation in the application problem: A certain school plans to purchase 20 bookcases and a batch of bookshelves (not less than 20). Information from two supermarkets, A and B, shows that products of the same model have the same price. Each bookcase costs $300, and each bookshelf costs $100. The discount policy at supermarket A is to give one bookshelf for free for every bookcase purchased, while the discount policy at supermarket B is to offer a 20% discount on all items. If it is stipulated that all items must be purchased from only one supermarket, under what circumstances will the school make purchases where the charges at both supermarkets are the same?

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