Table 6-12 on the textbook's Web site gives non seasonally adjusted quarterly data on the retail sales

Question:

Table 6-12 on the textbook's Web site gives non seasonally adjusted quarterly data on the retail sales of hobby, toy, and game stores (in millions) for the period 1992:1 to 2008: II.
Consider the following model:
Salest = B1 + B2D2t + B3D3t + B4D4t + ut
where
D2 = 1 in the second quarter, = 0 if otherwise
D3 = 1 in the third quarter, = 0 if otherwise
D4 = 1 in the fourth quarter, = 0 if otherwise
a. Estimate the preceding regression.
b. What is the interpretation of the various coefficients?
c. Give a logical reason for why the results are this way.
*d. How would you use the estimated regression to depersonalize the data?