We have monthly sales volume of Widget by Widgetaire for three years (36 months). We need to compute the 95% prediction interval of the forecasts for January, February and March of year 4 (periods 37,...

please use excel to solve this

Extracted text: We have monthly sales volume of Widget by Widgetaire for three years (36 months). We need to compute the 95% prediction interval of the forecasts for January, February and March of year 4 (periods 37, 38 and 39). Assume: optimal standard deviation = 35.1 units, forecasted sales for all these periods are 340.6 units, and z(0.025)= 1.96