If X and Y are sets of integers, X # Y denotes the set of integers that belong to set X or set Y, but not both. If X consists of 12 integers, Y consists of 18 integers, and 6 of the integers are in both X and Y, then X # Y consists of how many integers?	Choose one: A) 6 B) 16 C) 18 D) 30 E) 174

Rationale: "the number of integers that belong to set x only is 12 - 6 = 6 ; the number of integers that belong to set y only is 18 - 6 = 12 ; the number of integers that belong to set x or set y , but not both is 6 + 12 = 18 . answer : c ."
Answer: C