The problem is how to find the port number of My ORACLE server

The biggest trouble is to how find the port number of ORACLE server. My ORACLE is ORACLE7.x. If each ORACLE server has a file called "tnsnames.ora", how can I fail to find it after I logged into my ORACLE account. Is it possible that some ORACLE installation is incomplete so that "tnsnames.ora" is not installed or "tnsnames.ora" can be changed into other file name?

Thanks.

      
                                 Huaping Luo