You need this config on /etc/httpd/conf/httpd.conf if you have Passenger 3.0.12:
LoadModule passenger_module /opt/ruby-enterprise-1.8.7-2011.03/lib/ruby/gems/1.8/gems/passenger-3.0.12/ext/apache2/mod_passenger.so
PassengerRoot /opt/ruby-enterprise-1.8.7-2011.03/lib/ruby/gems/1.8/gems/passenger-3.0.12
PassengerRuby /opt/ruby-enterprise-1.8.7-2011.03/bin/ruby
You can try check this with:
#passenger --version
Phusion Passenger version 3.0.12
"Phusion Passenger" is a trademark of Hongli Lai & Ninh Bui.
and you need check the path:
ls /opt/ruby-enterprise-1.8.7-2011.03/lib/ruby/gems/1.8/gems/*