How to get total hour?

How to get total hour?

Name|| day||ActivityDate ||TimeIn || TimeOut ||
Ade || 20 || 2013-08-20 || 10:06:09 || 18:21:03 ||
Ade || 21 ||2013-08-27 || 11:00:34 || 18:06:56 ||
Ade || 22 || 2013-08-28 || 09:56:29 || 17:59:56 ||
This is my query :
select
tot=sum(DATEDIFF(hh ,TimeIn ,TimeOut )) as TotalHourAndMinute
from report
And error :
1582 - Incorrect parameter count in the call to native function 'DATEDIFF'
This is my table in datable.. I don't know how to get total hour like
TimeOut-TimeIn..
fyi, i have a lot of data in this table.. not only this 3..
i hope you guys clear...