Please show step by step how you solve it!

(4) Weekly sales of cases of fruit juice are given in the table below. a) [4 points] Compute forecast values for weeks 5 through 7 using a 4-period weighted moving average. Use weights 0.3,0.2,0.2,0.3. (Provide using a column in the above table.) b) [4 points] Compute the mean absolution deviation (MAD) for the forecasting technique in part a). (Use a column above for the absolute deviations.) c) Weekly sales of a widget are given in the table below. The previously computed forecasted value for Week 1 is also provided