The trend line = 1800 + 75t− 2t² and seasonal indexes shown in the table below were computed from five years of quarterly observations.Forecast the four quarterly values for next year.

Seasonal Indexes

Factors used to adjust data for seasonality, enabling comparisons across different times of the year by accounting for regular patterns of variation.

Quarterly Observations

Data points or measurements that are collected or reported every three months within a year.