This is one way.

DECLARE @TicketStartDate datetime

DECLARE @TicketEndDate datetime

SET @TicketEndDate = DATEADD(DAY, DATEDIFF(DAY, -1, GETDATE()) / 7 * 7, -1)

SET @TicketStartDate = DATEADD(DAY, -8, @TicketEndDate)

PRINT @TicketStartDate

PRINT @TicketEndDate

Also search this site for 'calendar tables'. Probably overkill for this situation but the method is great for date logic.