Need help with part b, please explain with formulas

The manager of the Petroco Service Station wants to forecast the demand for unleaded gasoline next month so that the proper number of gallons can be ordered from the distributor. The owner has accumulated the following data on demand for unleaded gasoline from sales during the past 12 months: Month Gasoline Demanded (gal.) October 800 November 725 December 630 January 500 February 645 March 690 April 730 May 810 June 1,200 July 980 August 1,000 September 850 a. Compute a 2-month moving average demand forecast for the months of December to September. Calculate MAD, MAPD and MSE. b. Compute the optimal 2-month weighted moving average demand forecast for the months of December to September. Calculate MAD, MAPD and MSE. C. Assume the demand forecast for October is equal to the actual demand of October, 800. Compute the optimal exponentially smoothed demand forecast for the months of November to September. Calculate MAD, MAPD and MSE. d. Assume the demand forecast for October is 800 and trend for October is 0. Compute the optimal double exponentially smoothed demand forecast for the months of November to September. Calculate MAD, MAPD and MSE. e. Compute linear trend line demand forecast for the months of October to September. Calculate MAD, MAPD and MSE. f. Compare the five forecasting methods by using MAD, MAPD and MSE and indicate which method is the best fit for the data based on MAD, MAPD (or MAPE), and MSE, respectively