Using the dataset you feel exhibits Trend and Seasonality use an additive decomposition model to:
a. Extract a seasonal index for each quarter,
b. Deseasonlise the data for each quarter
, c. Produce an unseasonalised and seasonalised forecast for each period,
d. Produce an unseasonalised and seasonalised forecast for periods n+1, n+2, n+3 and n+4,
e. Plot the actual, unseasonalised and seasonalised data on a single graph and comment on the results;