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 answer.
A) 11 B) 10 C) 12 D) 17 E) 19
10   10   (X + Y) â€“ (Y + Z) = 10   X â€“ Z = 10
<result>B</result>
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?