How do you call a function in a package via an sql query

I have got a function in PL SQ开发者_运维问答L called FUNCTION names_active(name_entity IN NUMBER) in a package called names_package how can I call it a query

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SELECT names_package.names_active(42) 
FROM dual

More details are in the manual:
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14251/adfns_packages.htm#sthref993