Using the airport exfreme, how do I add a network connected printer to my iPad3?

What is the make and model number of your printer?

Unfortunately, your all-in-one printer is not AirPrint compatible, so you cannot print from the iPad at the present time. See this Apple Support document for details:

http://support.apple.com/kb/HT4356

You might be able to use a workaround and install an App like Print Central on the iPad to see if that will allow printing, but there are no guarantees that this will work. More info here:

PrintCentral for iPad on the iTunes App Store