$($b$)$ Develop a three$-$week moving average for this time series. Compute MSE and a forecast for week $7.$

Do not round intermediate calculations. If required, round your answers to two decimal places.

$\backslash$table$[[$Week$,$Value,Forecast$],[1,17,],[2,13,],[3,15,],[4,11,],[,15,],[6,13,]]$

MSE: $,3\mathrm{.}2$

The forecast for week $7$: $$