Microsoft Project Standard 2013 License Key

I have three copies of Microsoft Project Standard 2013. I have three machines with the program installed. I have all the keys on their respective key cards. When the program was installed, no one noted which machine had which key.

I need to move the license from one machine to a new machine. I don't know which key to use. How do I find which (known, valid, and activated) key is on which machine so I can do the transfer? All machines work and are in my possession. When done, I will be using all three machines simultaneously, so I have to deactivate the installation on one machine to use it on the new one.

Thanks in advance,

Temp