from max date - 7 days

hallo !
can me somebody say, how i get from this select statement max date - 7 days.

select max(to_date(substr(PARTITION_NAME,6,10),'dd.mm.yyyy')) from dba_tab_partitions
where table_name='FRONTEND_TAB'

thank you

Oracle info: Oracle9i Enterprise Edition Release 9.2.0.8.0 - 64bit Production Received on Fri Oct 19 2007 - 04:39:20 CDT