SELECT avg(T1.sales) FROM journal AS T1 JOIN journal_committee AS T2 ON T1.journal_ID  =  T2.journal_ID WHERE T2.work_type  =  'Photo'
What is the average sales of the journals that have an editor whose work type is 'Photo'?
[Schema (values) (types)]: | journal_committee |  journal : journal_id (text) , date (number) , theme (text) , sales (text) | editor : editor_id (text) , name (number) , age (text) | journal_committee : editor_id (text) , journal_id (number) , work_type (text);