Wordpress Title Question

Hello folks!
In wordpress, how would I get the following title on my single posts:
Category Name: Post Title

<title><?php if(is_home()) { bloginfo('title'); } else { echo 'Variable here:'; wp_title(''); echo ''; echo ''; } ?></title>

Code (markup):

See, my code is right for the homepage, but for the single posts, I'm not sure what the variable is in Wordpress to make it the actual category. I just stuck something that says "Variable here", but I need the code that will display the post's category. What's the variable for that?

 

<title><?php wp_title(); { echo ' - '; } bloginfo('name');  ?></title>
 

PHP:

Try that

 

Well, that displays the title of the whole site. I'm looking to have only the category title, like so:
Category Title: The post title

 

If you are lazy like me try using the SEO Title Tag plugin

 

WOW...!

SEO title tag plugin is too good