I (have worked/ work) for ten years.?

Question 1 When somebody asks you " How long do you work?", which do you answer, (a) for 8 hours or (b) for 8 years. Question 2 I found lots of sentences, on the Internet, "I work for (number) years." What is the difference between "I have worked for ten years." and "I work for ten years"? Thank you!