b$.$ Use the in$-$sample forecast errors to compute MSE, MAD, and MAPE.

Note: Do not round intermediate calculations. Round final answers to $2$ decimal places.

$\backslash$table$[[$Performance Measure,Value$],[$MSE$,$MAD$],[$MAPE $(\%),]]$

c$.$ Make a forecast for period $21.$

Note: Do not round intermediate calculations. Round final answer to $2$ decimal places.

hat$(y{)}_{21}$

$\backslash$table$[[1,0,yt$