Answer: $1500 in total raise by the end of his 3rd year.
Explanation:
if every 6 months he gets a raise of 250$, double 3, your number of years. thats two raises per year. 3*2 is 6, meaning he receives 6 total raises in 3 years. 250*6 is 1500. he will make an extra $1500 by raise in 3 years.