Calculate formula in SQL Server function

I have a function that is supposed to calculate the total amount a customer has to pay in land tax. There is a table that contains the chargelines that apply to the customer and the definition table is shown below. Some of the charges are fixed, while others consist of a formula that says {Width_of_land}*{Length_Of_Land}*2080 . I need to calculate the Total amount based on a couple of charge lines that are a combination of fixed and variable (formula) inside a SQL function that is shown below. create table tblTarrifLine (ID bigint identity not null, Description varchar(100), UnitRate decimal(18,2), TarrifType varchar(100) default 'Fixed', Formula varchar(100)) go Insert into tblTarrifLine (Description,UnitRate,TarrifType,Formula) VALUES('Line Charge',30,'Fixed','') Insert into tblTarrifLine (Description,UnitRate,TarrifType,Formula) VALUES('Property Tax',1,'{W}*{L}*6','Formula') Insert into tblTarrifLine (Description,UnitRate,TarrifType,Formula) VALUES('Medical Surcharge',1,'{W}*{L}*3','Formula') Insert into tblTarrifLine (Description,UnitRate,TarrifType,Formula) VALUES('Education Surcharge',1,'{W}*{L}*2','Formula') create PROCEDURE CalculateAmount @Qty decimal, @W decimal, @L decimal AS BEGIN Declare @TotalFixedCharges decimal(18,2) Declare @TotalVariableCharges decimal(18,2) SELECT @TotalFixedCharges=sum(UnitRate)*1 from tblTarrifLine WHERE TarrifType='FIXED' print @TotalFixedCharges --calculate the @TotalVariableCharges END GO