A statistical program is recommended. The quarterly sales data (number of copies sold) for a college textbook over the past three years follow. (a) Construct a time series plot. What type of pattern exists in the data? There appears be an upward linear trend but no seasonal pattern in the data. There appears to be a seasonal pattern in the data and perhaps a moderate upward linear trend. There appears be a downward linear trend but no seasonal pattern in the data. There appears to be a seasonal pattern in the data and perhaps a moderate downward linear trend. (b) Use a regression model with dummy variables as follows to develop an equation to account for seasonal effects in the data. (Round your numerical values to the nearest integer.) x1=1 if quarter 1,0 otherwise; x2=1 if quarter 2,0 otherwise; x3=1 if quarter 3,0 otherwise Y^=