Use the following data to answer the question from $16-18$

$\backslash$begin$\{$tabular$\}\{|$l$|$l$|$l$|$l$|$l$|$l$|$l$|\}$

$\backslash$hline Period & Actual Demand & Forecast & & & & $\backslash \backslash$

$\backslash$hline $1$ & $5$ & $7$ & & & & $\backslash \backslash$

$\backslash$hline $2$ & $10$ & $6$ & & & & $\backslash \backslash$

$\backslash$hline $3$ & $5$ & $6$ & & & & $\backslash \backslash$

$\backslash$hline $4$ & $10$ & $8$ & & & & $\backslash \backslash$

$\backslash$hline

$\backslash$end$\{$tabular$\}$

Q$16.$ What is the Mean Squared Error $($MSE$)$ at the end of period $4?$