When does inversion happen

[Mr. Ayman Osman]

Dear Mr Mustfa
There are two confusing sentences
in question tag
workbook unit 10
b It’s very important that we eat healthy food, isn’t it/don’t we
The answer is isn't it?

2-

7- It's a must that all applicants follow the rules of the competition, ………….?

a) won't it b) don't they c) mustn't it d) mustn't they

Egypt 210 second session
In sentence 1 the tag was on the cfirst part
insentences 2 the tag was on the second part whyy
why
Best Regards