The task is to generate the correct answer for a given math problem.
--------
Question: Problem: the total age of a and b is 12 years more than the total age of b and c . c is how many year younger than a

Answer: 12

Question: Problem: the total age of a and b is 14 years more than the total age of b and c . c is how many years younger than a ?

Answer: 14

Question: Problem: in the xy - coordinate system , if ( m , n ) and ( m + 2 , n + k ) are two points on the line perpendicular to x = 2 y + 5 , then k = ?

Answer:
- 4