The data set plastics $($you need to library the fpp package to get the dataset$)$ represents

the monthly sales $($in thousands$)$ of product A for a plastics manufacturer for years $1$

through $5($data set plastics$).$ You need to load fpp package to have this dataset.

$($a$)$ Plot the time series of sales of product A$.$ Can you identify seasonal fluctuations

or a trend?

$($b$)$ Perform a classical additive decomposition using $"$stl$"$ function. Plot out the de$-$

composition. Try four combinations: $(1)$ s$.$window$=$"periodic", $(2)$ s$.$window$=$"periodic",

t$..$ indow$=5,(3)$ s$.$window$=$"periodic", t$.$window$=50$ and $(4)$ s$.$ window$=5,$ t$.$window$=50.$

Explain the differences you see in the plots.

$($c$)$ Compute and plot the seasonally adjusted data. You need to do this only for case

of s$.$window$=$"periodic",t$.$window $=50.$