A new amusement park is offering a family package that includes tickets for a family of four. The regular price for an adult ticket is $30, and the regular price for a child ticket is $20. The family package gives a 10% discount on the total cost. If a family buys the package and pays $180, how much did they save compared to buying the tickets individually? Let's think step by step and output the final answer within \boxed{}.
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