htaccess clean urls with with sub folder

I'm trying to create clean urls on my gallery website.

<http://sloanegalleryofart.com>

I was able to clean up general navigation. However, run in some hardcore difficulties while trying to configure sub folders

Curretnly my htaccess looks like so

Options +FollowSymLinks

RewriteEngine on



RewriteBase /



RewriteCond %{HTTP_HOST} ^sloanegalleryofart.com$ [NC,OR]

RewriteCond %{HTTP_HOST} ^www.sloanegalleryofart.com$

RewriteCond %{REQUEST_URI} !/

RewriteRule (.*) /$1 [L]



RewriteRule ^about/$ /about/about.php

RewriteRule ^contact/$ /contact/contact.php

RewriteRule ^shows/$ /shows/shows.php

RewriteRule ^artists/$ /artists/artists.php 

RewriteRule ^books/$ /books/books.php 

If I try to navigate from artists page sloanegalleryofart.com/artists to each individual artist it looks like so sloanegalleryofart.com/artists/artist.php?artist=Gleb-Bogomolov

When idealy i want it to be sloanegalleryofart.com/artists/Gleb-Bogomolov/ . Just cut out the whole " artist.php?artist= " out of the url

Thank you in advance !