Answer: He ends up making $16 
Explanation:
So if every 6 months he gets a raise of .50 
So if he works for 3.5 years or a total of 42 months you would want to divide it by 6 so 
42/6=7 so 7*(.50)=$3.50 so add that to the $12.50. 
So, $12.50+$3.50=$16 
Then the total ends up being a total of $16