Question: Quarterly billing for water usage is shown below.

Year

Quarter 1 2 3 4

Winter 6 66 68 73

Spring 103 103 104 120

Summer 152 150 -62 176

Fall 73 72 78 88

Assume that the seasonal index has been calculated as follows:

Season Seasonal Index

1 0.666

2 1.035

3 1.568

4 0.730

Assume that the data was deseasonalized and regression analysis was used to develop the following trend line: Ft = 92.686 + 1.32325t

Forecast the water usage billing for Year 5.