Press escape then :wq! for write and quit (forced)
If it complains about being read-only you need to be root (sudo vi /etc/passwd)
tbh I predict that removing the x won't work anyway, and it means your system has a totally open admin account with no security, and although vi is my favourite editor it's probably not worth learning unless you want to get really into linux. nano is quite a good one that's a bit more intuitive.
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