CozyforU is a manufacturer of down jackets. Its director of sales wants to develop seasonal forecast of sales that accounts for any trend or seasonality. The following table shows sales (in millions of units) of one product model for the past 16 seasons. Season 2017 2018 2019 2020 Winter 97.15 96.25 96.10 95.35 Spring 56.35 55.90 56.05 57.25 Summer 35.05 36.10 35.35 34.90 Fall 67.90 70.00 67.60 67.45 a. (Points: 8) Determine the slope and the intercept of the least square regression line starting with Winter of 2017 as period 1 and ending with Fall of 2020 as period 16 (for example, Fall of 2017 will be period 4 while Winter of 2020 will be period 13). b.(Points: 12) Use the regression results to calculate the seasonal index for each season of each year. From the indices for all sixteen seasons, calculate the average seasonal index for each season. c.(Points: 5) Using the regression line from part (a) and the average seasonal indices from part (b), derive a sales forecast for each season of the year 2021 that accounts for both trend and seasonality.

Season	2017	2018	2019	2020
Winter	97.15	96.25	96.10	95.35
Spring	56.35	55.90	56.05	57.25
Summer	35.05	36.10	35.35	34.90
Fall	67.90	70.00	67.60	67.45