There are several ways to determine, where Apache has been installed on your Linux/Unix system and what are other imporant paths for it (WWW root, configuration etc.). You can use this nice blog entry, which in general means executing
ps -ef | grep apache to determine path and then running
/usr/sbin/apache2 -V with proper path (replace
/usr/sbin/ part) to determine Apache configuration details.
If everything else fails, try to help yourself with Installation and setup of the Apache Web Server (Linux) document.