Understanding query and explain plan

hello Gurus,

     I have a query which is slow and dure long time for a statement "update". ( I join the tkprof )

i see in the explain plan that i have "MERGE JOIN CARTESIAN" and i see it too in my advisor's report.

I see next "An expensive cartesian product operation was found at line ID 6 of the explain plan".

|   5 |	NESTED LOOPS	|	|   108 | 11664 | 66001   (4)| 00:00:15 |
|   6 |	MERGE JOIN CARTESIAN	|	| 19598 |  1416K| 10869   (5)| 00:00:03 |
|   7 |	NESTED LOOPS	|	|	|	|	|	|

My question when advisor tell to me that is the line 6 then how can i find the table which have not any link with other tables ?

( Except do a list of all the table and control all the link )