How to Find Others Admin Passwords after gaining admin priviledge?

This is the situation, i've gained admin priviledges on this machine at uni, there are two account Info30 (the default account with admin priviledge) and Student (the one i've hacked) now i got to find out the Info30 password, i don't want to reset the Info30 password i just want to know it.

All the other pc in uni have the same password of Info30 and knowing the password would give me a more "forensic" approach.

The system is Win7 x64.