Averaging weekly data from daily data from multiple spread sheets - functions ?

I am working on a project that my boss wants and I would like to know if there is an function or formula I can use to help.

Currently I collect daily proudction data for multiple tasks that an employee does thru out the day. All employees have their own tab on a excel workbook (see attached - weekends are in gray). I can easily get the monthly average for.

The problem is I now have to produce a weekly average as well as the monthly average that will then be linked into charts on a seperate spread sheet. Is there a way to use any funtion or forumula instead of going thru each employees tasks by week and summing it manually?