The closing value of the AMEX Airline Index for each trading day during a one-year period is

Question:

The closing value of the AMEX Airline Index for each trading day during a one-year period is given in the file P12_17.xlsx.
a. How well does the moving average method track this series when the span is 4; when the span is 12?
b. Using the more appropriate span, forecast the closing value of this index on the next trading day with the moving average method.