Re: back up and help out
If I am someone's "back-up" (noun) I am the person who can do their job while they are out.
I was Karen's back-up while she attended the conference.
Sometimes I back up Mary as well.
When Karen got a really large project, she needed someone else to work on it with her. I helped her out.
Do you see how those are not the same verb?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.