Interpretation of explain plan

Our developer deployed a new feature of application to production without even letting me know. Appearantly, it has not been tested under dev system. I am really mad. But that's another story. Now, the new feature has slow down the application. The query in use as follows:

SELECT NVL(RESERVE1, '0') AS RESERVE1, NVL(RESERVE2, '0') AS RESERVE2

FROM M_PRT

WHERE DEL_FLG = 0

AND DRAWING_NO LIKE 'xxxyyyzzz'

AND LINE = 'x';

I found out this table only have primary key index and does not have any other indexes. Some of the column need to be indexed has null values.