The overall age of X and Y is 10 year greater than the overall age of Y and Z. Z is how many decades younger that X?  Choose the correct choice from the following answers:
A) 11
B) 10
C) 12
D) 17
E) 19

Rationale: "b 10 ( x + y ) â € “ ( y + z ) = 10 x â € “ z = 10"
Answer: B