Evaluate a seasonally adjusted trend forecasting model.

Note: Round all of your answers to $\backslash (\backslash$mathbf$\{3\}\backslash )$ decimal places except "Absolute Percent Error" which should be rounded to $\backslash (\backslash$mathbf$\{2\}\backslash )$ decimals. b$.$ What are the MAD and MAPE?

Note: Round your answers to $\backslash (\backslash$mathbf$\{2\}\backslash )$ decimal places.

c$.$ What are the monthly indexes?

Note: Round your answers to $4$ decimal places.

d$.$ Forecast sales for January, February, March, and April of $2022.$ Note: Round your answers to $3$ decimal places.