The Following Trend Line and Seasonal Indexes Were Computed from Five

Essay

The following trend line and seasonal indexes were computed from five years of quarterly observations: $=1800+75 t-2 t^{2}$ . $$\begin{array} { | c c | } \hline \text { Quarter } & S I _ { t } \\\hline 1 & 0.575 \\2 & 0.825 \\3 & 1.225 \\4 & 1.375 \\\hline\end{array}$$ Forecast the four quarterly values for next year.