Oracle SQL Trigger not getting created

I have a table passenger as shown below

Column       Null?        Type
------------------------------------
NAME          -          VARCHAR2(20)
ID          NOT NULL     NUMBER
ADDRESS       -          VARCHAR2(20)
CHARGES       -          NUMBER

I am learning triggers and I want to create a trigger that updates charges as charges + 100 before a new insert is done. Here is the trigger I created.

create or replace trigger flight
before insert on passenger
for each row
set new.charges = new.charges + 100;
/

However, I am getting the error ORA-04079: invalid trigger specification. I have tried replacing new with :new, adding begin & end blocks, but none of them seem to work.

Answer

Invalid syntax.

create or replace trigger flight
  before insert on passenger
  for each row
begin
  :new.charges := :new.charges + 100;
end;
/