Develop a multiple regression model for sales as a function of different quarters, income (INC) and unemployment (NRUR).You can define as following: a dummy variable Q1 = 1 for each first quarter and Q1 = 0 otherwise; a dummy variable Q2 = 1 for each second quarter and Q2 = 0 otherwise; and a dummy variable Q3 = 1 for each third quarter and Q3 = 0 otherwise. Identify the regression equation for your model:

Period	Sales $	Inc	NRUR
Mar-09	153907	475	6.9
Jun-09	127732	534	6.5
Sep-09	93209	574	6.5
Dec-09	118203	622	6.4
Mar-10	145611	667	6.3
Jun-10	129976	702	6.2
Sep-10	95219	753	6.3
Dec-10	105210	796	6.5
Mar-11	164592	858	6.8
Jun-11	113201	870	7.9
Sep-11	105932	934	8.3
Dec-11	132182	1010	8
Mar-12	174200	1066	8
Jun-12	152918	1096	8
Sep-12	132290	1162	8
Dec-12	152419	1187	7.8
Mar-13	182764	1207	7.5
Jun-13	162921	1242	7.1
Sep-13	132961	1279	6.9
Dec-13	152971	1318	6.5
Mar-14	193271	1346	6.2
Jun-14	172312	1395	5.5
Sep-14	152281	1443	5.3
Dec-14	192314	1528	5
Mar-15	221938	1613	4.8
Jun-15	219223	1646	4.7
Sep-15	182342	1694	4.5
Dec-15	201921	1730	4.4
Mar-16	253901	1755	4.2
Jun-16	243976	1842	4
Sep-16	203338	1832	3.9
Dec-16	246723	1882	3.8
Mar-17	265532	1914	3.5
Jun-17	223008	2027	3.5
Sep-17	219976	1989	3.4
Dec-17	243338	2056	3.4
Mar-18	274456	2032	3.3
Jun-18	253382	2204	3.2
Sep-18	227764	2190	3.1
Dec-18	241138	2342	3.1