4. (20 Points) You have been given the most recent 20 quarters (t) of data on the sales (x) of brand A phones as the following table. You decide to use the multiplicative Holt-Winter method to forecast future sales. Your initial estimates of alpha, beta, and gamma are 0.2, 0.3, and 0.2. However, you lose some data by coincidence. Quarter 1 2 3 4 1 151 228 433 2 165 223 269 3 Year 336 4 240 383 5 471 a) Luckily, you have processed the data and recorded that 2(t) =210, 20 20 ?,(t2) =2870, ?,(x) =8060, ?i(xt) =101315, ? (x) = 4261270 . t=1 Assume x = So+Got, what is your estimate of So and Go? (6 pts) b) What is your estimate of T[2]? (4 pts) c) Assume that your calculated average seasonal values are as follows: [] = 0.6489, T[2] = as calculated above, T[3] = 0.9180, T[4] = 1.5997, Calculate one- step ahead forecast for the first three quarters. (10 pts)