In this level we have two files passwords.old and passwords.new and the password is the only line that differs between the two.
For this we can use the diff command, which lists the differences between two text files.
diff passwords.old passwords.new
The output is the line that has changed. The top is the original and the bottom is the change. The bottom one is the password: hga5tuuCLF6fFzUpnagiMN8ssu9LFrdg