Gashol (A Mixture of Gasoline and Methyl Alcohol)sales in Iowa

Essay

Gashol (a mixture of gasoline and methyl alcohol)sales in Iowa City have been recorded over the past 10 months as shown below:
$$\begin{array} { | c | c | c | c | c | c | c | c | c | c | c | } \hline \text { Manth } & \text { Jan } & \text { Feb } & \text { Mar } & \text { Apr } & \text { May } & \text { June } & \text { Juy } & \text { Aug } & \text { Sep } & \text { Oct } \\\hline \text { Sales } & 75 & 72 & 81 & 92 & 90 & 105 & 112 & 107 & 110 & 93 \\\hline\end{array}$$
-Compute the four month centered moving average.