step by step please

A manager has boon using a certain forecasting technique to forecast demand for word processing units for the past five periods. Actual and forecasted amounts are shown below. He had difficulties in identifying whether the used technique is better than the weighted moving average (WMA) with 0.5 being the weight with the most recent 0.3, 0.2. Calculate the total absolute error for the manager's forecast? (Noter write the answer as a number with 2 decimal places only. og 12.50, 55.83 , 12.00) Period Demand forecasted 1 90 98 2 85 87 3 91 95 4 92 7 95 88