4. Number of elements in the intersections of sets

If $n(A \cup B \cup C) = 63$, $n(A) = 35$, $n(B) = 32$, $n(C) = 31$, $n(A \cap B) = 22$, $n(B \cap C) = 18$, and $n(A \cap C) = 12$, then find out $n(A \cap B \cap C)$.

 

$n(A \cap B \cap C)$ $=$