Generate 1-step-ahead forecasts for the last two years of your sample (2018 & 2019) using a () model with window lengths = 3 and = 12. Make a plot of actual against forecasted sales. Tip: Make sure to generate exactly 24 forecasts covering the period 2018-19, by using observations from earlier periods.

Frequency: Monthly
observation_date	S4248SM144NCEN (sales)
2016-01-01	8650
2016-02-01	10324
2016-03-01	12109
2016-04-01	11423
2016-05-01	12242
2016-06-01	13685
2016-07-01	10955
2016-08-01	12705
2016-09-01	12276
2016-10-01	11910
2016-11-01	13021
2016-12-01	14425
2017-01-01	9045
2017-02-01	10453
2017-03-01	12481
2017-04-01	11489
2017-05-01	13537
2017-06-01	14717
2017-07-01	11395
2017-08-01	13373
2017-09-01	11871
2017-10-01	12663
2017-11-01	13202
2017-12-01	14191
2018-01-01	9493
2018-02-01	10329
2018-03-01	12569
2018-04-01	11805
2018-05-01	14012
2018-06-01	14420
2018-07-01	12518
2018-08-01	14073
2018-09-01	12231
2018-10-01	13727
2018-11-01	13949
2018-12-01	15308
2019-01-01	10616
2019-02-01	10976
2019-03-01	12472
2019-04-01	13098
2019-05-01	14573
2019-06-01	14277
2019-07-01	13484
2019-08-01	14205
2019-09-01	12992
2019-10-01	14427
2019-11-01	13773
2019-12-01	16197
2020-01-01	10659
2020-02-01	11350
2020-03-01	13410
2020-04-01	12334
2020-05-01	14111
2020-06-01	16215
2020-07-01	15757
2020-08-01	15400
2020-09-01	15644