Question $3(20$ pts$)$:

The worksheet Q$3$ contains data on the demand of a particular product for each month of the previous year.

a$)$ Forecast demand for the first month of the current year using alinear trendline $($a fitted linear trend graph with estimated equation should be included as part of your analysis$)$; and forecast demand for the first month of the current year using an exponential smoothing model with $=0\mathrm{.}6.$

b$)$ Calculate MAD, MAPD and Cumulative Errors based on the forecasting results for the previous year by each model. Which one of the two models do you prefer? Type your answers$/$explanations below your analysis.