$($b$)$ Compute MSE using the average of all the data available as the forecast for the next period. What is the forecast for month $8?$

The MSE is to be calculated again, but this time will be based on the forecasts made using the average of the data. The given data follow.

$\backslash$table$[[$Month$,1,2,3,4,5,6,7],[$Value$,17,25,21,26,22,21,26]]$

The forecast for month $2$ will be the observed value from month $1.$ The forecast for month $3$ will be the average of the observed values from months $1$ and $2.$ The forecast for month $4$ will be the average of the observed values from months $1,2,$ and $3.$

Complete the column$-$of forecast values using this method.

$\backslash$table$[[$Month$,$Value,Forecast Value$],[1,17,,],[2,25,17,],[3,21,\frac{17+25}{2}=21,0$