A particular date, if it falls on the X day out of the 7 days in a week, in a year Y, then it should fall on the (X+1) day in the year (Y+1), provided that the year (Y+1) is not a leap year. If it is a leap year then the date falls on the (X+2) day in the year (Y+1).
Now since, 6th March 2005 falls on Monday and 2005 is not a leap year, so 6th March 2004 should fall on Sunday.