B. 41
Given: S = {x | x is a positive multiple of 3 less than 100} and P = {x | x is a prime number less than 20}
To find: n(S) + n(P)
S = {x | x is a positive multiple of 3 less than 100}
⇒ S = {3, 6, 9, 12, 15,……, 99}
n(S) = 99/3 = 33
P = {x | x is a prime number less than 20}
⇒ P = {2, 3, 5, 7, 11, 13, 17, 19}
⇒ n(P) = 8
n(S) + n(P) = 33 + 8 = 41
Hence, answer is 41