please help with MAD a=.9 _ sales?

please explain how to do it in excel!

snagunis pop gewe wang semper sistere c a smoothing constant (a) of 0.30 and a starting forecast of 410.00, the following sales forecast has been developed: D Forecasted Year Sales Sales 2005 450 410.00 2006 495 422.00 2007 516 443.90 2008 570 465.53 2009 584 496.87 The MAD for a forecast developed using exponential smoothing with a 0.30 is 75.34 sales (round your response to two decimal places). Forecasted sales for years 2006 through 2010 using exponential smoothing with a=0.60 and a starting forecast of 410.00 are (round your responses to two decimal places): Year 2005 2006 2007 Forecasted Sales 410.00 434 470.6 2008 2009 2010 497.84 541.14 566.85 The MAD for a forecast developed using exponential smoothing with a = 0.60 is 52.28 sales (round your response to two decimal places) Forecasted sales for years 2006 through 2010 using exponential smoothing with a 0.90 and a starting forecast of 410.00 are (round your responses to two decimal places): Year 2005 2006 Forecasted Sales 410.00 446 2007 2008 2009 2010 490.1 513.41 564.34 582.03 The MAD for a forecast developed using exponential smoothing with a=0.90 is sales (round your response to two decimal places)