center formula and right text align

I am trying to write a paper and I need to number some formulas I use for easy reference like in this image http://puu.sh/4cgQG.png

I cannot figure out how to get a formula center aligned and some text right aligned on the same line. Could someone please tell me how to do this?

Re: center formula and right text align

I don't remember now if certain environments I mention below come from the vanilla LaTeX or from the amsmath package, so I'll assume that amsmath is included.

Unstarred environments for display math, such as *align* and *gather*, add numbers to equations. Starred environments like *align** and *gather** don't. There is an unstarred environment for a single equation: *equation*. As far as I understand, *equation** is equivalent to \[ ... \]. You can add a tag where none is provided by default or replace a tag using the \tag command. Its argument is typeset in text mode and is surrounded by parentheses unless you use \tag*. You can also suppress tags with \notag.

I recommend reading the amsmath user guide or a chapter about math in some good book on LaTeX such as The LaTeX Companion. It's well worth the time.