Remove file elder than 90 days

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http://www.unix.com – I have crontab job a tar file to a directory ( tar -cvf /tmp/backup/or.`date +%m%d%y`. /ora/db/* ) , it will do it every day . Now I don't want to keep too much files , I just want to keep the file for 90 days , can advise if I want to remove the backup file which are elder than 90 days , can advise what can I do ? Thanks (HowTos)