Use Venn diagram: Let A = 42, B = 34, C = 20 Let overlaps: \[ A \cap B = 24, \quad B \cap C = 10, \quad A \cap C = 12, \quad A \cap B \cap C = 4 \] Apply:
\(\text{Total} = A + B + C - (A \cap B + B \cap C + A \cap C) + A \cap B \cap C = 42 + 34 + 20 - (24 + 10 + 12) + 4 = 96 - 46 + 4 = {54}\)