Automate Week Ending Date

How do i automate, by stored procedure, generating the "week ending" date using a field data.

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CREATE TABLE [dbo].[t_Work_Hours] (
[WorkHoursID_PK] [int] IDENTITY (1, 1) NOT NULL ,
[PeopleID_FK] [int] NOT NULL ,
[JobID_FK] [int] NULL ,
[StartTime] [datetime] NULL ,
[EndTime] [datetime] NULL ,
[Title] [nvarchar] (1) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
[WeekEnding] [datetime] NULL ,
CONSTRAINT [PK_t_Work_Hours] PRIMARY KEY CLUSTERED
(
[WorkHoursID_PK]
) ON [PRIMARY] ,
CONSTRAINT [FK_t_Work_Hours_t_Work_People] FOREIGN KEY
(
[PeopleID_FK]
) REFERENCES [dbo].[t_Work_People] (
[PeopleID_PK]
)
) ON [PRIMARY]
GO
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What i have tried has'nt even been close to a solution.
UPDATE dbo.t_Work_Hours
SET WeekEnding = DATETIME ( ??? , StartTime) . I have no idea where to go!

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WorkHoursID_PK, PeopleID_FK, JobID_FK, StartTime, EndTime, Title, WeekEnding
7, 40, 3, 11/1/2005 6:00:00 AM, 11/1/2005 4:30:00 PM, J, (NULL)
8, 43, 3, 10/31/2005 6:00:00 AM, 10/31/2005 4:30:00 PM, F, 11/6/2005 11:59:00 PM
9, 43, 3, 11/1/2005 6:00:00 AM, 11/1/2005 4:30:00 PM, F, 11/6/2005 11:59:00 PM
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