how can I make money with my flashgames?

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Please help me with such a question: how to make money with flash games? I've a friend who's good at creating flashgames, and he runs a website of his own myhappygames.com which offers 3000+ more games. But now he's developing new flashgames and want to make extra money with it, but how to? He has the original game engine source and all the codes, but don't know how to make money with them. Please give suggestions and also recommended some websites, thanks a lot!