Problem 18-20 (Algo) In this problem, you are to test the validity of your forecasting model. Here are the forecasts for a model you have been using and the actual demands that occurred: WEEK 1 2 3 4 5 6 FORECAST 870 765 865 865 915 890 ACTUAL 915 915 965 815 815 1,040 a. Use the method stated in the text to compute the MAD and tracking signal for each week. (Negative values should be indicated by a minus sign. Round your "Tracking Signal" to 1 decimal place and all other answers to the nearest whole number.) Week Forecast Actual Deviation Running Sum of Forecast Errors Absolute Deviation Sum of Absolute Deviation Mean Absolute Deviation Tracking Signal 1 870 915 2 765 915 3 3 865 965 4 865 815 5 915 815 6 890 1,040 b. Decide whether the forecasting model you have been using is giving reasonable results. The forecasting model is acceptable The forecasting model is unacceptable