Question

what is the intersection of the three sets?
A=[1,3,5,77,9]
B=[1,2,3,5,7]
C=[1,2,5,8,9]
__________________________
ANSWERS:
a. [1,5]
b.[1,2,5]
c.[1,3,5,7]
d.[1,2,3,5,7,8,9]

Answer 1

You write down a list (set) of elements which appear in ALL THREE sets A, B and C.
If it is missing from any set, skip it.
Then put your list between braces i.e. { and } (not [ and ]).

If you want to check answers, do not diminish the importance of your answer by writing a letter. Write out (or at least copy and paste) the value of the answer.

Answer 2

b?