Invalid Insert Statement In The Function

Dear Friends.

I m trying to use the insert statement with in the function !
and i m getting this errror !

Server: Msg 443, Level 16, State 2, Procedure GetTotalCOst, Line 16
Invalid use of 'INSERT' within a function.

Please help me how to rectify it and how i can use the Insert statement with in the function !

Here is the code for the function.


create function dbo.GetTotalCOst(@varWork_no as numeric,@varSubWork_no as numeric)returns numeric as
begin
Declare @valCost integer
Declare @TotService integer
Declare @TotParts integer
Declare @TotLabour integer
Declare @TotTravel integer
Declare @TotSubContract integer
select @TotService= isnull(sum(quantity*costprice),0) From SB_Service_Suppply_Details where work_no=@varWork_no and subwork_no=@varSubWork_no
select @TotParts= isnull(sum(quantity*costprice),0) From SB_PARTS_dETAILS where work_no=@varWork_no and subwork_no=@varSubWork_no
insert into dbo.SB_InvoiceCostingService values(@TotService,@TotParts,1,1,1,1,1,1)
return (@valCost)
end