Oracle Function

CREATE OR REPLACE FUNCTION OFFICE.fbill_getbalance (billid NUMBER, total NUMBER)
   RETURN NUMBER
IS
   paid      NUMBER;
   balance   NUMBER;
BEGIN
   balance := total;
--get total paid
   SELECT SUM (n_paidamount)
     INTO paid
     from tbnk_payoutbillconn i
    WHERE i.n_billid = billid AND i.s_billorpur = 'B';
--get balance of bill
   balance := NVL (total, 0) - NVL (paid, 0);
   RETURN balance;
EXCEPTION
   WHEN NO_DATA_FOUND
   THEN
      RETURN balance;
   WHEN OTHERS
   THEN
      RETURN balance;
      RAISE;
END fbill_getbalance;