The overall age of X and Y is 18 year greater than the overall age of Y and Z. Z is how many decades younger that X?	Options.
A) 11
B) 15
C) 12
D) 17
E) 18

Rationale: "e 18 ( x + y ) â € “ ( y + z ) = 18 x â € “ z = 18"
Answer: E