An associate at a macroeconomic consulting firm is studying annual regional GDP data over the last 30 years. For each year, she has obtained GDP data for the two main economic regions of the country: South and North. She estimates the regression model: Y = a b1T b2D1 b3TD1 where Y is the GDP for that region for that year T is the year D1 = 1 if the data is for the North region and 0 for the South region Note: Please note that if something is a difference between two quantities, you need to clearly specify whether something is higher or lower as well as compared to what. (a) Provide a precise economic interpretation for b1. [3 points] (b) Provide a precise economic interpretation for b3. [5 points]