There are a couple of ways to do this, here is the way that I usually use. Depending on the version of ubuntu you're currently running, you might need to install aptitude. You can do that by opening a terminal and typing the following:

sudo apt-get install aptitude

Once aptitude is installed then you would type the following to determine the version that would be installed or is installed depending.

sudo aptitude show jetty

Hope this helps!

Chris