You only need to add it ONCE to your root .htaccess file. If you don't already have an .htaccess file then you need to create one, but I'm pretty sure you should already have one.
Only this code:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^e-hacking.com
RewriteRule (.*) http://www.e-hacking.com/$1 [R=301,L]