Keep your answers BRIEF. Observe the points per question. It's class reunion time - ten years since high school graduation! You want to impress your high school classmates with the fancy regression technique you have picked up while taking ECON 320, but secretly you want to understand whether your career choice at a prestigious Atlanta Quant firm, Hootchie River Associates (HRA), paid off. To this end, you ask your 400 classmates to submit their number of years of education and their salary Y as measured in K USD (i.e., Y = 100 they make 100 K gross a year) in a sealed and anonymized envelope. To your surprise, everyone in your high school class did either work immediately (i.e., zero years of additional schooling), went to community college (2 years), or graduated after exactly 4 years from college, and there is a sizeable group of each. Given the knowledge your acquired in ECON 320, you call the random variable "additional years of schooling" X and, mindful of what you learned in ECON 320, you set up the salary model a