Let xt represent the annual glacial varve series (varve in astsa package). (30 points, 10 points each) (You can refer to file week3_glacier_estimation.R for part of code.) a Plot the data and comment on the stationarity and whether/what transformations are needed to make it stationary. b Make the neccessary transformation. Plot the transformed data and its ACF, PACF. Comment on the stationarity and discuss which model you would use. c Fit an MA(1) to the transformed data using R function arima. Report the estimated model. d Plot the ACF and PACF for the residual. Comment