(i) n (B)
As we know,
n (A ∪ B) = n (A) + n (B) – n (A ∩ B)
By substituting the values we get
42 = 20 + n (B) – 4
42 = 16 + n (B)
n (B) = 26
∴ n (B) = 26
(ii) n (A – B)
As we know,
n (A – B) = n (A ∪ B) – n (B)
By substituting the values we get
n (A – B) = 42 – 26
= 16
∴ n (A – B) = 16
(iii) n (B – A)
As we know,
n (B – A) = n (B) – n (A ∩ B)
By substituting the values we get
n (B – A) = 26 – 4
= 22
∴ n (B – A) = 22