Final answer:
In the provided regression equation for demand and price, a $1 increase in price leads to a decrease in demand by 3000 units, reflecting the law of demand.
Step-by-step explanation:
The regression analysis between demand (y in 1000 units) and price (x in dollars) resulted in the following equation: y = 9 - 3x. This equation suggests that for every $1 increase in price, there is a corresponding decrease in demand. Specifically, if the price is increased by $1, the demand is expected to decrease by 3.thousand units.
The law of demand, which states an inverse relationship between price and quantity demanded, supports this finding. As the price rises, the quantity demanded tends to decrease, and vice versa. Therefore, the correct answer to the student's question is: 2) decrease by 3 units (or, more accurately, by 3000 units since the units of y are in 1000).