Stacy needed to buy drinks for her daughter's birthday party but couldn't decide what to serve. She surveyed her daughter's school friends to see what they liked. 30 said that they liked soda, 25 said that they liked iced tea, and 31 of her friends said that they liked lemonade. Out of those votes, 16 said that they liked soda and iced tea, 13 said they liked iced tea and lemonade, and 21 said that they liked soda and lemonade. 8 friends liked all three drink options. 6 did not like any of the drink options. How many friends did Stacy survey?

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