Vacation destinations often run on a seasonal basis, depending on the primary activities in that location. Amanda Wang is the owner of a travel agency in Cincinnati, Ohio. She has built a database of the number of vacation packages (Vacation) that she has sold over the last twelve years. The following table contains a portion of quarterly data on the number of vacation packages sold.

a. Estimate the linear regression models using seasonal dummy variables with and without the trend term. Which is the preferred model. Then, use the preferred model to forecast the quarterly number of vacation packages sold in the first two quarters of 2020. (Round coefficient estimates to at least 4 decimal places and final answers to 2 decimal places.)

Year	Quarter	Vacation
2008	1	480
2008	2	127
2008	3	1294
2008	4	653
2009	1	964
2009	2	564
2009	3	1429
2009	4	1105
2010	1	189
2010	2	438
2010	3	1337
2010	4	524
2011	1	463
2011	2	260
2011	3	1372
2011	4	760
2012	1	320
2012	2	983
2012	3	1672
2012	4	763
2013	1	761
2013	2	389
2013	3	1637
2013	4	772
2014	1	651
2014	2	749
2014	3	1048
2014	4	500
2015	1	596
2015	2	755
2015	3	1195
2015	4	494
2016	1	212
2016	2	472
2016	3	1561
2016	4	1008
2017	1	531
2017	2	849
2017	3	1094
2017	4	456
2018	1	385
2018	2	392
2018	3	1101
2018	4	534
2019	1	646
2019	2	709
2019	3	1263
2019	4	903