What is the answer to no.3

Answer 1

Assuming you mean Section 5: More Types, part 2: dictionaries...question 3:

The page just before that tells you exactly what to look for: mutable vs. immutable. In the question, one of those types is mutable and cannot be used.

Note that every time you try, the app rearranges the answers; this may be blocking you.

Answer 2

No.3 in what

Answer 3

8