please solve by formula calculation not excel thank you

3- Favors Distribution Company purchases small imported trinkets in bulk, packages them, and sells them to retail stores. The managers are conducting an inventory control study of all their items. The following data are for one such item, which is not seasonal. (a) Use a trend projection to estimate the relationship between time and sales (state the equation). (b) Calculate forecasts for the first four months of the next year. Month Sales 1 2 3 4 5 6 7 8 9 10 11 12 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 51 55 54 57 50 68 66 59 67 69 75 77