A local bookstore is keeping a database of its customers to find out more about their spending habits and so that the store can start to make personal recommendations based on past purchases. The first 5 lines of the database appear in the accompanying table. a) For each variable, would you describe it as primarily categorical, or quantitative? If quantitative, what are the units? If categorical, is it ordinal or simply nominal? b) Are these data a time series, or are these cross-sectional? Explain briefly