Zephyr is a manufacturer of paper towels, napkins, and toilet paper. The manager of the Zephyr factory in South Carolina needs your help as an analyst to forecast sales of their Select-A-Size Paper Towel packs. The sales data for this product in the past 12 months is shown below (Note that month 1 refers to sales made 12 months ago. Month 12 refers to sales made last month.):

Month	Sales (in millions of packs)
1	1335
2	1334
3	1340
4	1342
5	1353
6	1358
7	1375
8	1376
9	1407
10	1423
11	1470
12	1498

You have realized that the sales for Select-A-Size Paper Towel packs have been increasing over the past year. You have learned that the double exponential smoothing method can account for such a trend in the data.

1. (Points: 10) Use double (trend-adjusted) exponential smoothing method to forecast sales for months 2 to 13, assuming S₁ = 1335 and T₁ = 15 and set = 0.8 and = 0.2.
2. (Points: 4) Plot the actual sales, the double exponential smoothing forecast, and the forecast obtained using simple exponential smoothing in Problem 2 with = 0.8 for months 2 to 12 on the same graph.
3. (Points: 11) Compute the MAD and MSE for months 2 to 12 for the double exponential smoothing forecast and compare them with those from simple exponential smoothing in Problem 2(c). Based on your calculations, which approach is better in this particular case, single or double exponential smoothing? Explain.