how to use/migrate a dll (built by me) in silverlight?

I have a class library built on .net 3.5, I wanted to use it in a silverlight project and it told me that I must build it against silverlight runtime, anybody knows how to do this ?

c开发者_运维知识库an I migrate it, or should I create a new silverlight project and rewrite it or something ?

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You need to create a Silverlight Class Library:

_{(source: c-sharpcorner.com)}