ขอความช่วยเหลือเกี่ยวกับการสร้าง Trigger ของ SQL Server Database

CREATE TRIGGER TR_Calc_Value ON Enrollment AFTER INSERT, UPDATE AS
BEGIN
   UPDATE E 
   set MonthlyPayment = (

      select 0.05 * SUM(Salary) 
      from Family FAM 
      inner join Filiation F 
      on FAM.IDFamily= F.IDFamily 
      where F.IDStudent = I.IDStudent
      )

   from Enrollment E
   inner join inserted I
   on E.IDEnrollment=  I.IDEnrollment