$n(A - B) = n(A) - \dots$

در هر حالت، با توجه به اطلاعات داده‌شده، مقدار عبارت موردنظر را بیابید: الف) $n(A) = 12, n(B) = 17, n(A \cap B) = 3$ | $n(A \cup B) = ?$ ب) $n(A) = 25, n(B) = 21, n(A \cup B) = 38$ | $n(A \cap B) = ?$ ج) $n(B) = 20, n(A - B) = 30$ | $n(A \cup B) = ?$ د) $n(A) = 42, n(B') = 74, n(A - B) = 31$ | $n(A \cup B') = ?$ ه) $n(A) = 400, n(A') = 300, n(B - A) = 50$ | $n(A \cup B') = ?$ و) $n(A - B) = 70, n(B - A) = 75, n(A \cap B) = 9$ | $n(A \cup B) = ?$