3. The sales of a product over the past six months are shown in the table below. Month January February March April May June Sales 150 120 140 160 170 160 a. (10 pts.) Make a forecast for July using the exponential smoothing method with the smoothing constant a = 0.7. For initial forecast, use the Nave method. b. (10 pts.) Calculate the MAPE (Mean Absolute Percentage Error) of the exponential smoothing method in part (a)