All of your suggestions are good.
You can also start off by saying one of:
Sorry. I can't hear you.
Sorry. I didn't catch that.
Then follow it up with any of:
It's a bad line.
The line is bad.
You're breaking up.
You're distorting.
You're cutting out.
There are a lot of other ways of saying the same thing.
Read full article from telephone - What do you say when you talk over phone but you can't quite hear what other person says? - English Language & Usage Stack Exchange
Khan Academy - K12 Maths Resources Online | Free Kids Books
Khan Academy Maths has an amazing set of comprehensive online maths resources. These K12 online maths resources include lessons and quizzes perfect for teaching and testing mathematics in K-12 schooling.
These Khan Academy mathematics resources are separated into grade 1 to grade 8 then high-school maths is separated into subjects.
Each subject has topic lessons that include videos, sometimes reinforced with articles, and lots of practice exercises, at the end there's a test section to check your knowledge.
Read full article from Khan Academy - K12 Maths Resources Online | Free Kids Books
