The utilities data set contains information from utilities bills for a personal residence over a number of years. This problem explores gas usage over time.

a) Make a scatterplot of gas usage (ccf) vs. time. You will need to combine month and year to get a reasonable measurement for time. Such a plot is called a time series plot.

b) Use the groups argument (and perhaps type=c('p','l'), too) to make the different months of the year distinguishable in your scatterplot.

c) Now make a boxplot of gas usage (ccf) vs. factor (month). Which months are most variable? Which are most consistent?

d) What patterns do you see in the data? Does there appear to be any change in gas usage over time? Which plots help you come to your conclusion?