How can I find abt the amount of PL/SQL stored.
For user SCOTT run:

select ceil(sum(vsize(text))/1024) "PL/SWL in Kilobytes" from dba_source where owner='SCOTT';

My SGA is sized at 400000000.
buffers r 90000
block size is 8k
any views reg this.
As I don't know anything about your DB, I could only say that the values a bit high but if you have the memory.... How much RAM do you have?