There are a couple of options:
1. Make the datasource with the office the primary, then use a table calculation to sum up the totals.
2. Use Tableau's Primary Groups feature to "push" the office information from that source into your original primary data source.
A possible 3rd option is to do a join in your data source, but it looks like you're using Tableau Server data sources so that might not be feasible.
I did a writeup on this for this forum thread: http://community.tableau.com/thread/118319
And I put together a demo workbook for you.
Thanks a lot Jonathan,
I use the 1rst option and its work
i afraid to use the second because the Tableau's Primary Groups not referesh when the data change