The accompanying data file contains monthly observations for 5 years. Click here for the Excel Data File a. Calculate the 12-month centered moving average. (Do not round intermediate calculations. Round your answers to 2 decimal places.) b. Calculate the ratio-to-moving average. (Do not round intermediate calculations. Round your answers to 2 decimal places.) c-1. Calculate the seasonal indices for April and November. (Do not round intermediate calculations. Round your answers to 4 decimal places.) c-2. Interpret the seasonal index for April. (Do not round intermediate calculations. Round your answer to 2 decimal places.) c-3. Interpret the seasonal index for November. (Do not round intermediate calculations. Round your answer to 2 decimal places.)