denote by n(X) the element number of a finite set X. Let A, B and C sets such that n(A ∪ B) = 8, n(A ∪ C) = 9, n(B ∪ C) = 10, n(A ∪ B ∪ C) = 11 and n(A ∩ B ∩ C) = 2. Then, n(A) + n(B) + n(C) is equal to:

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