What is formula or value of
n ( A ‘ ∩ B ‘ ∩ C ‘)
surely your math text explains this. If not, google will provide many discussions of the topic, as in
math.libretexts.org/Bookshelves/Combinatorics_and_Discrete_Mathematics/Combinatorics_Through_Guided_Discovery_(Bogart)/05%3A_The_Principle_of_Inclusion_and_Exclusion/5.01%3A_The_Size_of_a_Union_of_Sets