Continue your analysis of the weekly sales data for ToothPaste. Remember, it is in dataset "groceries.csv" which contains weekly units sold for three grocery items: ToothPaste (100ml container of toothpaste), PeanutButter (340g. jat of crunchy peanut butter), and Biscuits (200g., 10 finger package of shortbread cookies). The dataset contains the variable Date defined as the first day of the week for the sales period. Answer the following questions a) Graph the lag plot of the ToothPaste series and its first lag. Interpret the graph. What does it tell you about autocorrelation for this series? b) Compute and plot the first 15 lags of the autocorrelation function for ToothPaste weekly sales and discuss if the series shows evidence of serial correlation. c) Use the Ljung Box test to hypothesis that ToothPaste weekly sales have significant serial correlation. d) Discuss the importance of weak stationarity for time series analysis and describe a method to analyze whether a TS is stationary