I'm currently applying for a TEFL course, however there is one particular area that I am struggling with. The question is; "Identify which of the following sentences contains errors and correct them. Then explain why you think the speaker made the mistakes in each case" The sentence examples that are provided are;

1) We've lived here since three years.
2)It's high time we finish this.
3) He asked me what can he do for me.
4)The hotel's comfortable and the weather's attractive.
5) There was far less people at the match than I expected.
6)If I was you, I'd get more sleep.

If anyone could help identifying the errors, but more importantly help explain why the speaker would have made those mistakes, it would be very much appreciated.