You can also type ZZ (uppercase, so hold Shift) to write and quit. But for all of the above you have to be in normal mode, so if it doesn't work, try pressing Esc first.

:x for write and quit. But I think the more appropriate one in this situation will be :q! which will force quit without saving any modifications, since someone who doesn't know how to exit vim probably doesn't want to save whatever modifications they made (probably by mistake).

Good catch!

This is where the critical Linux adoption advice is happening. :)