2 lists data to add in 3list using with infopath and its depend on (cascade dropdown) and use with Linq to get the values to list3

http://basquang.wordpress.com/2010/03/29/cascading-drop-down-list-in-sharepoint-2010-using-infopath-2010/

LINQ To SharePoint: Performing CRUD operation on Cascade Lists

http://www.dotnetcurry.com/showarticle.aspx?ID=684

http://blogs.msdn.com/b/bharatgupta/archive/2013/03/07/create-cascading-dropdown-in-browser-enabled-infopath-form-using-infopath-2010.aspx