Data on the Last Three Years of Demand Are Available

Short Answer

Data on the last three years of demand are available as follows: $$\begin{array} { l l l l l } &&& { \text { Season } } \\\text { Year } & \text { Spring } & \text { Summer } & \text { Fall } & \text { Winter } \\\hline \text { Three years ago } & 18 & 10 & 26 & 42 \\\text { Two years ago } & 26 & 18 & 34 & 50 \\\text { Last year } & 34 & 26 & 42 & 58\end{array}$$ What is the linear regression trend line for these data (t = 0 for spring, three years ago)?