In the default configuration, Apache will be set to display the version information
on most of your error pages. The easiest way to verify what version of Apache
you have, is to visit a link to a file that does not exist. Such as http:// domain.com/unknownfile.txt
If for whatever reason, you do not see the version listed, you can find out from
the command line.
You will want to run the binary with the -v option. This will give you a short response,
that includes both the version number, and the date the binary was built.