Tables :: Designing Fee Receiving System - Due Field To Show Balance

I did using below:

One table with Student Basic Records with Course name and Total Fee

Tabel name Student_Rec and Fields are below
ID, StudentName, Course Name, RollNo, Total Fee

then another table name Fee_Details for receiving dues in installments.
ID, RollNo, FeeDue, FeePaid, Comments

Now i want the FeeDue Field should show the Balance feedue of each student

I mean it automatically check total fee due from student_Rec table and also check all previous entries for the same rollnumber in Fee_details Table and show the pending amount as FeeDue.