Help in varchar column calculation

SmithToronto , normally I would let the backend/frontend, in plain SQL it's to error-prone; but this should work:

Create table ##Calculation (Calc1 numeric (10,2), calc2 numeric (10,2), Calc3 numeric (10,2), Calc4 varchar(40))

insert into ##Calculation 
values (6,7,8, 'calc1+calc2+calc3');

DECLARE @sql nvarchar(4000);
SET @sql = (SELECT N'SELECT C.Calc1, C.Calc2, C.Calc3, ' + C.Calc4 + N' ' +
                   N'FROM ##Calculation AS C'
            FROM ##Calculation AS C);
EXEC sp_executesql @sql

GO

DROP TABLE ##Calculation;
GO