File not working properly in my server .htaccess

Hi all,
I have to change the display of the PHP files extension as html files like .html on the address bar on the browser. I am using the following code for this in text file and save it as .htaccess.
RewriteEngine On
RewriteRule ^(.*)-([0-9]+).html$ viewstudent.php?id=$2
RewriteRule aboutus.html$ aboutus.php
RewriteRule careers.html$ careers.php
RewriteRule services.html$ services.php
RewriteRule consulting.html$ consulting.php
RewriteRule enquiry.html$ enquiry.php
RewriteRule contactus.html$ contactus.php
Unfortunately it is not working. It just shows PHP file extension only when I test. Is there any problem in my code, please suggest me, if any one can do.
Thanks,
Jim Crowley
