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Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

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James wants to promote his band on the internet. site a offers website hosting for $4.95 per month with a $49.95 startup fee. site b offers website hosting for $9.95 per month with no startup fee. for how many months would james need to keep the website for site a to be a better choice than site b?