Use the following model to forecast quarterly sales ($ 000) for a start-up (where time is rescaled to begin at zero and Q2, Q3, and Q4 are dummy variables for the indicated quarters), and answer the following questions.
y = 15.1 + 10.5 t - 5.0 Q2 - 7.2 Q3 + 7.5 Q4
a) For the first quarter of the time series, what are the sales?
b) What is the quarter that on average has the lowest level of sales over the time frame of the series?
c) What is the quarter that on average has the highest level of sales over the time frame of the series?
d) Interpret the coefficient of the dummy variable named Q4.