Procter & Gamble, a multinational consumer goods corporation, is experiencing significant growth in various markets.

Required: Develop a seasonal sales forecasting model from the following historical sales data. Use multiple regression analysis. Predict the next year's sales and calculate the standard errors of the forecasts.

Historical Sales Data
Sales, millions of liters	Year	Calendar month
3400	1	1
3450	1	2
3500	1	3
3550	1	4
3600	1	5
3650	1	6
3700	1	7
3750	1	8
3800	1	9
3850	1	10
3900	1	11
3950	1	12
4000	2	13
4050	2	14
4100	2	15
4150	2	16
4200	2	17
4250	2	18
4300	2	19
4350	2	20
4400	2	21
4450	2	22
4500	2	23
4550	2	24
4600	2	25
4650	3	26
4700	3	27
4750	3	28
4800	3	29
4850	3	30
4900	3	31
4950	3	32
5000	3	33
5050	3	34
5100	3	35
5150	3	36