Oracle HTTP Server is developed using Apache server as base. So if you have Oracle Application Server installed in your environment and if you want to know the in built Apache version then you can use either of the approaches.
1. Goto $ORACLE_HOME/Apache/Apache/bin and execute ./httpd -v or ./httpd -version.
In most of the environments you may not be succesful with the above command then you can use 2nd approach as given below.
INST_LOC is a regitry entry, which was used by the Installation: